Man, some depressing advice here from some grumpy old men, who assume your friend is an idiot…
The great Americana roadtrip experience never dies, and shooting pool along the way, will be great fun! US gas prices, lodging & food are still cheaper than EU and of course in todays world, no one is going to make $, but he’ll have great fun. There is a scene to still be found virtually anywhere you go, if expectations aren’t too high.
Among other considerations, I’d make sure to ID spots that are fun to see outside of just pool, then wrap pool into the plan. I think ShootingArt & u12armrel’s advice is good; the Southeast and gulf coast would be my picks for most dense old school action. FL is great fun on all fronts and endless options everywhere you go. Vegas & Phoenix, AZ are the well known hotspots and must be sampled, but generally pretty crappy places to visit non pool wise. Roadtripping up the west coast from San Diego to Seattle is a must-do IMO, and plenty of spots to still get in trouble.
If you make it to Northern CA, PM me for contact info, he’s welcome to crash at my place and plenty of great life adventures & action around San Fran & Sacramento.
Coming from EU, he’s probably mostly a big table rotation player, so the US bar/barbox scene and poolhall 1p vibe will most likely be novelty “growth areas” for him.
You’d think/hope that given all the whingeing on AZB about the death of US pool - there would be a more welcoming roadplayer/couchsurfer community vibe for him, but don’t be discouraged!