I just had a ‘suspension check' at a well known national 4x4 shop. The ‘found’ a bunch of stuff that may or may not be a problem.

They called out the lower drag link, the upper and lower ball joints and control arm bushings as having movement. I tried to reproduce their findings and I couldn’t move any of this stuff.

If these things need replacement I have no complaints. The Jeep is 20 years old and has 140,000 sometimes hard offroad miles. I just don’t want to just start throwing parts at it. The steering is a little sloppy but not scary.

My real question is

What is the best was to diagnose these suspension components?

Best bang for the buck is ball joints. Since you can't grease the lowers and they carry most of the weight of your jeep, they're going to need replacement soon anyway. Get them right out of the equation. You may be surprised.

They're going to "find" everything they can reasonably cite. You can replace everything mentioned for a very reasonable price if you do it yourself.

I'd start with the ball joints (as Dave mentioned) and then see how the Jeep rides and if it's still not to your liking, move on to the other items.

Look at it yourself.

LIft a tire and put a prybar under the tire and lift up and down. Is there movement? If yes ball joints are bad.
WIth tire off the ground grab at 12 and 6 and push in and out. Is there movement? If yes wheel bearings are bad
WIth tires on the ground is there any rotational movement on the drag link and tie rod? If yes they are worn and could use replacement.

Shops are always about OH MY GOD IT NEEDS FIXING when it doesn't but it is up to you to decide how bad it is and how safe you want to feel