What seismic wave will be the most useful in determining the extent and thickness of the earths interior layers?

Did you mean wave(s)?
If so, p and s waves should be your answer.
Hope this helps!

Historians are researchers of the past or people who understand the history of people. with this field, they must possess qualities such as being unbiased, patient, efficient reader, has a knack for logic and critical thinking and reasoning, disciplined, open-minded, resourceful, with good analytical ability, good reasoning skills and problem solving!

Ansradar; im guessing here; good luck : )