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Get all 3rd Party dependencies module is using in Maven

We have a multi-module maven project. I have a use case where I want to know to get a list of all the dependencies which is being used in code with version:
If its declared in pom and being used.
Not declared in pom but still being used (transitively imported).
Bonus would be if the approach can exclude the deps which are being declared in pom but not being used in the code.
Please suggest the best way to achieve this. TIA.

Just use the mvn dependency:tree command.

There's the Maven Dependency Plugin:
The dependency plugin provides the capability to manipulate artifacts. It can copy and/or unpack artifacts from local or remote repositories to a specified location.
with its tree goal:
Displays the dependency tree for this project.
Regarding your bonus there's the analyze goal:
analyzes the dependencies of this project and determines which are: used and declared; used and undeclared; unused and declared.
and the analyze-only goal:
is the same as analyze, but is meant to be bound in a pom. It does not fork the build and execute test-compile.

How version of lib defined in classpath?

i have hirarhy of modules.
I set up version of hibernate-validator as 6.1.5.Final
But when i build project version of library another
maven dependencies: tree ouput
org.hibernate:hibernate-validator:jar:5.3.4.Final:compile
I can not understand how it works.
I put all dependency tree here https://paste2.org/CwB2H4W2

Problems with dependencies should always bring you to the "Dependency Hierarchy" Tab of your POM.xml. There you will see your projects dependencies, and dependencies of that dependencies.
If I had to guess I'd say there you will find a module providing the dependency you think you don't use.
Further information to maybe change this:
First declared dependencies get used first. So if you define your dependency before the Module that brings the other dependency in, Maven should select yours.

Integration testing of Maven Plugin submodule

I have Maven project with multiple submodules. One of these submodules, let's say submodule X depends on all other submodules, as it is Maven Plugin that integrates everything else.
Now I want to use this Maven Plugin during verify stage in my parent POM to do real run of it over entire project (kind of eating own dogfood).
Unfortunatelly I'm getting error:
The projects in the reactor contain a cyclic reference
So how can I make such dogfood integration test for a Maven Plugin submodule?

I would review aggregation and inheritance: they are indeed two different concepts in Maven often used in combination but which can however be used in a complete separated manner as well.
In this case, your plugin submodule is certainly defined as a module in the aggregator pom (that is, it is a submodule). But I also presume the plugin submodule also has as parent pom the aggregator pom as well (that is, the aggregator pom is also the parent pom, which is a normal approach, but not always required).
Is the latter required? You could keep on having the multi-module/aggregator approach without necessarely having the aggregator as parent of the plugin submodule. As such, the plugin subModule would still be a module of the aggregator pom but it would not have as a parent the aggregator pom, decoupling it from it and as such breaking the cyclic dependencies.
Possible drawback: in the aggregator pom you were also defining common things (dependencies management, properties) required also in the plugin submodule. If the case, you would then need to duplicate/review these common settings only for the concerned submodule.

Small suggestion from my side. Cyclic means you have some transitive dependency in your modules. Can please check the dependency tree of your modules and resolve the circular dependency first.

Multi-module IntelliJ project with maven - How to add dependencies from one module to another?

Let's say I have a maven project which has some maven modules inside.
My main module depends on the other modules, so when I compile the main module they should be compiled together.
The question is, how to add these modules as dependencies to the main module?
I know if I have a custom lib that I want to use with maven, let's say a utilities project, I have to compile the jar of the project, do a mvn install:install-file on it to install it on the local repository and then add it to the pom.xml.
Do I have to do this with all my modules and add the dependency to the pom.xml on my main module? Because if it should be done like this, there will be a lot of work to do when changing code on the other modules.
What is the best practice to use avoid the trouble of compiling/installing the modules to local repository?

The question is, how to add these modules as dependencies to the main module?
The same way you add any other dependency to your maven project. By adding group id, artifact id and version to <dependency> element
Do I have to do this with all my modules and add the dependency to the pom.xml on my main module?
If your main module depends on some module A then only the pom of the main module should contain dependency declaration towards module A. You do that for all the dependencies of your module.
I don't know what you mean by "a lot of work when changing the code on other modules". Maven has nothing to do with code changes, it just builds the projects whatever they look like at the given moment...
What is the best practice to use avoid the trouble of compiling/installing the modules to local repository?
Any project that you invoke mvn install on gets built and it's jar copied to local repository. That's all you need to do to get the jar into the repo. This will also put all the dependent jars, if available, into the local repo.
As for best practices for multi module projects:
If your parent project (the one that has modules inside) has <modules> section that lists the modules of your application, and modules are in subdirectories of your parent project, then you simply mvn install (or whatever you want to do) the parent project and that will cause all the modules to be built in order defined by declared dependencies between them. That means that if your main module has dependency on module A, then module A will be built before the main module. This way you can build and install all your modules with one command. On the other hand this approach makes more tight coupling between modules which is not desired in some cases, so it depends on your use case whether it is a good approach or not.

Is there some way to clean the maven dependencies?

I am working in a Maven project which has about 250 jar dependencies. Approximately Four out of five dependecies are not direct dependencies, I mean, they are dependencies of our dependencies (i.e jasperreport has about 8 dependencies).
Also, I suspect that there are some jar which we don't need to the project because they were old dependencies of old tool that we needed in the past but they were replaced by others.
What I need is:
To detect what jars of my pom.xml are not needed by the
project.
A way of removing the indirect jars from my pom.xml.
*Note: I'd swear that some time ago I manage to the indirect jars were downloaded by the direct dependencias, but I can't find how.

You're after mvn dependency:analyze:
Analyzes the dependencies of this project and determines which are: used and declared; used and undeclared; unused and declared.
This will let you remove any dependency which is not directly used from your pom. The dependencies that are used will still bring in their transitive (indirect) dependencies, as required.

I'm not really sure if you need to remove some dependencies of any of your direct dependencies or just want to clean jars downloaded.
If your problem is the first one, you can use "exclude" for that dependencies -> http://maven.apache.org/guides/introduction/introduction-to-optional-and-excludes-dependencies.html
If it's the second one, just remove your .m2/repository content and rebuild again your project