Hi Marco,
Thanks for the update.
We suggest you to get the grid value and the selected index of the MultipleColumnDropDown using its element id. Also, you can get the cells values of the grid using the selected index of the row.
Please refer the following code snippet:
[JavaScript]
Please refer the sample from the following link:
SAmple384822358.zipLet me know if it helps.
Regards,
Jaffer