I can't quite tell from the drawings in the manual, but it looks like the VIDEO OUT jack takes a simple RCA video plug. If that's correct, and if your external video device doesn't have RCA audio/video jacks, you could buy a connector that has RCA audio/video plugs on one and another type of plug on the other end-- VGA, DVI, or whatever your video device can accept.
The manual indicates that you can set the outgoing video signal to NTSC or PAL as required, so any monitor or TV that's compatible with either of those two standards (depending on which one is used in your country) should work. The internal display uses 320x240 dots, so you'll want to get a monitor or TV with an old 4:3 picture aspect ratio, as opposed to one with a 16:9 widescreen aspect ratio, unless you don't mind either having the display stretched or having it displayed with black bars on the side. I think most modern TVs should be able to handle old 320x240 picture signals, in order to maintain compatibility with old video game consoles (among other things); and most computer monitors can certainly handle a variety of screen resolutions.