EDC for my father

[Nap]

$350 basically takes you straight to the top-tier production knives, and the vast majority of knives you can simply remove the clip, so there's no lack of options. A few options I can think of would be the Lionsteel TRE, Kizer Gemini, Spyderco Paramilitary2 (Basic version shown here, but for your budget you can hunt down a wide variety of runs in different high-end steels) Spyderco Manix2LW in S110V, Spyderco Domino (G10/CTS-204p version) and Benchmade 940-1.

A couple of other notable options are the ZT0562 and the venerable Sebenza 21.

Any of these, plus the Spyderco Sage (1, 2, the CF version of the 3, and maybe even the 4 if he goes for the old-fashioned look). Since you mention ZDP-189, the Delica and Endura in that steel are top-notch if you want a working knife more than you want looks.