Friend said when she took her car(2008 T5) to a mechanic he said her engine oil was leaking on the exhaust, how much I don't know?

Would that be a engine gasket problem? Would that be something I could fix or just let the mechanic fix it?

 

there are several things that can cause oil leaks but to figure out whether its a DIY project or not, start by cleaning up the oil mess then see where the fresh oil is coming from (look for the highest point).

What make/model car does she have?

Usually the exhaust is not anywhere near an oil leak except for turbo cars where the most common leak is the oil return line seal (a $.10 part) which can spray oil all over the manifold and back of the engine. To access you will need to remove the turbo's heat shield and you'll see a hard line running from the turbo back into the block. search youtube for vids on how to if this sounds like your issue. Note it would take a shop about 1 hour's work to fix this ~$125-150.

Other possible causes get more complicated - clogged PCV can push oil out the oil filler cap , a loose dipstick and then there are engine seals. Most of the PCV tubing is on the front of the engine and the major seals are on the nose (under the timing belt cover) or above the transmission (rear of the cylinder head). For oil to get on the exhaust from these, it would have to be a big enough leak to wet the underside of the motor and then get blown back to the exhaust pipe. This is where you'd want to clean the engine up first.