So I just bought what i believe to be a 2000 jeep cherokee limited 4.0 I6, the only thing questionable is that it has 218,000mi. Ive always been a skeptic of high mileage vehicles like that, especially since I've never had one, but it seemed as if the PO had taken good care of it. Now it has trail rated badges which confused me, I was under the impression only wrangler Grand Cherokee got the badge.
With XJ's Mileage is a distant third consideration to maintenance and rust. In 00-01's it's even farther behind b/c of the 0331 head. In that year, to save weight, Chrysler used an aluminum head on the cast iron block. It's not a problem in normal operating conditions BUT if the vehicle overheats, they expand at different rates and the head can crack next to cylinder 3, letting coolant into the engine and oil into the coolant.
Check your coolant for a mucky brown goopy quality that might indicate it has oil and/or rust in it. That's a sign of a cracked head That and a badly rusted unibody are pretty much the only reasons an XJ should be dead before 400k barring a wreck. Even if you DO have a cracked head the car will run longer than you'd think like that, giving you time to either decide on a repair, build a stroker to replace it when it finally goes, or just put it back on the market to buy another vehicle you're more comfortable with.
You SHOULD however either get a report from the PO or check all of the 150ish thousand mile items. Cooling system probably wants a flush/refresh, all moving parts in the steering should be checked (ball joints, bushings and TRE's), and check for signs of fluid leakages or any weird sounds around the diffs and wheels (signs of worn seals/bearings). You should also check all the fluids, especially the tranny/transfer case and differential fluids. for signs of burning. It'll smell bad and look a little blackened. Not black, just a little darkened like someone dropped some charcoal dust in it. You didn't put your location on your profile, but if you're anywhere with a bit of rust you should check your floorpans and all the metal lines, most especially your fuel lines.
None of those things are really XJ-specific, it's just a list of things to go through with any high-mileage car. As I mentioned earlier the only thing the XJ is more sensitive to than any given car is a well-maintained cooling system.
Side note: XJ's never got a trail-rated badge from the factory. Someone got one from a junkyard or a vendor because they liked the idea of having it.