Hi Alejandro,
This is what I do to find the closed point to a coordinate in a mesh.
Open the mesh in BlueKenue
Add a single point set in Bluekenue, with the Mesh view displayed.
Edit the point coordinates to the required values, the point will move to the required coordinate, the you can select the closest mesh point to this point by visual inspection. You may change the property of the point to monochrome and increase the size to get better visibility of the point in Bluekenue view.
Hope this help
With Best Regards,
Gourish