I have a editable grid with 3 columns: a id, question, grade. I need the id col

If your use case is you have value in id and question column and user select grade from dropdown so for which row user selected grade you want to save id of that particular row then you don't have to show id to users, you can use this code in saveInto of dropdown field.

a!save(ri!SelectedIds,tointeger(index(index(local!Items,where(not(apply(isnull(_),local!Items.grade))),{}),"id",{})))

here SelectedIds is the variable of type list of number(integer) where you want to save selected ids.
Items is the type of cdt where you have these three columns.

If your use case is you have value in id and question column and user select grade from dropdown so for which row user selected grade you want to save id of that particular row then you don't have to show id to users, you can use this code in saveInto of dropdown field.

a!save(ri!SelectedIds,tointeger(index(index(local!Items,where(not(apply(isnull(_),local!Items.grade))),{}),"id",{})))

here SelectedIds is the variable of type list of number(integer) where you want to save selected ids.
Items is the type of cdt where you have these three columns.