You'll have to use the field names instead of labels.
For example Location is "location", Assignment group is "assignment_group" and Assigned to is "assigned_to".

They're all reference fields so you should be able to populate them correctly when you provide a sys_id available in servicenow.

Requested for (requested_for) is not a field on catalog task table, but instead is actually on the requested item table, so you can't modify that for the catalog task. If you want to change it then you'll have to change the value on requested item, but that will change it for all the tasks as well.