Is there a "best" screen resolution to choose for running Sketchup Pro 2019 on a 15.6 inch 4k laptop?

Snapping-to precision would seem to be easier to “hit the mark” on a lower resolution than full 4K on a small screen. No? Or do I misapprehend the technology here? It seems to me that if you’re trying to hit the established guide point with the cursor in such a densly crowded bunch of pixels per square centimeter the program might have an easier time handling it if the ‘target’ guide point were represented by more pixels…as I expect it might if 1080p were chosen/set in the screen settings while using Sketchup.

Also a few of the menus that pop up in sketchup are evidently not optimized yet for viewing on a small 4k screen. Most of the menu boxes are just as I am used to seeing them on my old 1080p Hp Workstation. But on my new 4K screen occasionally a tiny menu will pop up and the text is about 1/32 inch font that is impossible to read.

A screen that small isn’t really intended to be used at 100% enlargement. Instead of messing with screen resolution you could try setting a larger display scale. SketchUp supports the Windows screen scale settings up to 150%. My Asus Zenbook has an about 14" fullHD screen, and I run even that at 125%, as I do with my 32" 4K monitor at home.

“…you could try setting a larger display scale.”

Is that done in Windows 10 settings, Nvidia settings, or Sketchup settings?

Windows settings ideally.
Anything larger than 150% may cause some issues with some software menus etc
But in your case you probably do need 200% to read everything clearly.

Windows settings: Right-click on your desktop, select Display settings, Scale and Layout