If its a lifter sometimes you can find out which one by using a mechanic's stethoscope or a long handled screw driver and listen along the top of the valve cover. If you take the valve cover off you can check each one by placing your finger on the top of the rocker while idling the engine and you will feel the bad one but.....be prepared for a oily mess unless you use some rocker clips to keep the oil from squirting out. If its a lifter, sometimes they can be cleared by pushing down on the rocker of the loud lifter with something solid like a hammer handle while the engine is running...like I said this sometimes works to clear the lifter.
If you don't already have one, get a Manual from Haynes or Chilton, this will help you out.
Replacing or cleaning out a lifter is not hard, will need a special tool you can get from auto parts store or a good long handled magnet to get it out.
2013 WRANGLER SPORT 2 DR., V-6 ,AUTO,HARD TOP
)1994 Jeep Wrangler 2.5L, Bestop top
/w steel half door and slider windows
5 speed, 2.5" lift, 31" tires,rack lights