Here is a little sample. It handles 2 sort of complications.
One regards when the grid''s comtext menu is displayed versus when a cell control''s context menu is displayed. The sample does a little work to make both cases display the same menu.
The other is a problem getting the row, col of the click. For some reason, Control.MousePosition is not working for me to get the proper right click (I suspect the Framework is tweaking this to display its popup). But this problem can be worked around by handling CurrentCellMoved and just tracking the focusRow and focusCol. (Depending on setting, you may need to add a grid.MouseDown handler to track this as well. The sampledoes not need this.)