I dont think there is a direct way to do this but i see 2 options.
1. Use a Custom Widget to inspect the DOM and check the innerHTML value of the control bar buttons
2. Make a Microflow which should take the CURRENT SELECTED ITEM of the Page in that grid. Then Since you know the LIMIT per page already(No of rows which is set in the Data grid widget), first get all the elements of this Entity from DB. Then group them in the batches where batch size is same as LIMIT size(No of rows). Then find in which Batch the CURRENT SELECTED ITEM is present.
The Batch in which the item is present is the Page Number. Page Size is nothing but the limit that you set in the grid.
Hope this helps you or gives you some hints for the solution. Good luck.