Hello @thanos,
Welcome to ITK! 
To visualize the transform, the 3D Slicer transform visualizer is a fantastic tool get a perspective into the transform, visualized with arrow or sphere glyphs, grids, and isosurfaces in both 2D and 3D. Slicer supports reading and writing transformation in ITK’s HDF5 transformation file format.
If the transformation is not already a displacement field, it can be converted into a displacement field over the image’s domain with itk::TransformToDisplacementFieldFilter. The displacement field is a multi-component ITK image. The displacement vector value at specific locations can be probed with the GetPixel() method. Interfaces are available in Python (has a Matlab-like interface) to probe these values.
I hope this helps.
Matt