The EventTask table is joined to it's child table called Event.
In the Parent table (Event)
Don't you mean "in the CHILD table (Event)?"
In any case, you would use Set Field to enter the correct ID number from __pkEventTask, not EventTaskType. (This happens to be what the value list does as well. It enters the Field 1 value into the field even though it may display the field 2 value.)
How you determine which ID number is the correct value, is something I can't tell you from your post.