There is no successor function as the workflow changed. While it was previously necessary to call ProGtolDataGet and then call other ProGtoldata*() functions to extract information from that Gtoldata, you can now use new functions to directly manipulate the ProGtol item.
Example for getting the type of a ProGtol:
ProGtol my_gtol; // lets pretend it's pointing to a valid item
ProGtoltype type; // that's what we want to get
Old workflow
ProGtoldata data;
ProGtolDataGet(&my_gtol, &data);
ProGtoldataTypeGet(data, &type);
ProGtoldataFree(&data);
New workflow
ProGtolTypeGet(&my_gtol, &type);
So the replacement of ProGtolDataGet depends on what you're actually doing with the gtol. Use the new functions to achieve the same goal as before.