Hey guys, any idea what can cause zero compression in one cylinder? I took it in today and they told me I have no compression in cylinder#2 but they don't know what the cause would be without disassembling it

 

You might ask them to do a leak down test.

What this does;
bring the piston for that cyl up to the top of it's compression stroke
all valves should be closed now.
They remove the spark plug for that cyl insert a fitting with a low pressure air supply and listen for where they would hear air leaking out.
If they hear it in the oil fill hole, piston ring/piston failure
If they hear air leaking into the intake manifold, intake valve problem
If they hear air leaking into the exhaust , an exhaust valve problem
You don't state the year and engine, should have that..
Did this engine ever overheat?

 

To cause zero compression would likely be a stuck or severely burned valve.If you had low compression, there would be more possibilities.