Rookie question regarding spar

You can have an A&P look inside the fuselage to make sure the bulkheads are ok. But even if that part of the fuselage is ok I’d want to know what incident caused them.

The center spar can be visually inspected. However, the area in your pictures (didn't see any wrinkles in those) is the empennage. Wrinkles there could represent having hit the tail on something (flying or not) causing bending in the braces that help stiffen the aluminum of the empennage. That can also be inspected visually from the inside to determine if one (or more?) of the braces are bent.

Weird location for wrinkles. They would worry me. They’re pretty far from the center spar. I’d sure want to know how they got there!