Need 240V in the shop, is it already in this OLD panel box?

That’s a 240 double pole breaker. With #10 wire it should be a 30 amp.
If your planning on an air compressor and lights and receptacles you need to
up the wire size. Looks like a 3/4” conduit coming up in the box do you know if it’s conduit all the way from the main panel? Wire size dictates what size breaker you
can safely use.