how to make dialog window resolution free

That's plain impossible. A change in resolution will affect an application's depiction in some way. Always.

You can, however, make some aspects resolution-independent at the expense that some others will have to change in order to compensate.

You can make your application window a fixed size in pixels. At a larger resolution, it will maintain its size in pixels. All controlls will still have their sizes and distances to each other. But the monitor space not covered by your application will get larger.

You can make your application window fullscreen. At a larger resolution, it will remain fullscreen, still totally covering the monitor. But empty space, filled with window background colour could show up along the right and bottom edges.

You can make your application fullscreen and its controls cover all the client space. At a larger resolution the controls will have to grow to keep occupying all available space.

So you need to specify which version you would prefer your application to behave.

Isn't WPF resolution independant? I've never used them so far but I read something like that...

I am intersted in knowing purpose of the problem??