Most 2012 Jeep Grand Cherokee ticking noises are the result of one (or in some cases, multiple) faulty rocker arms. Rocker arms are pieces of the engine that transfer the motion of a pushrod onto a valve. Over time, the rockers may get some normal wear and tear that causes grooves or indentations. When they move, it creates the ticking noise that you describe.
Unfortunately, bad rocker arms can cause the engine to slowly deteriorate and lose efficiency over time, so you should probably get them replaced ASAP. The amount of the repair will vary depending on how many faulty rocker arms your Grand Cherokee has, but you can reasonably expect to spend between $600 to $1,000 for the repair.