It's not EGA: 16kB of RAM, 6845 CRTC, a character ROM and discrete logic means its got to be CGA. The second RCA jack could be for a light pen but those usually had a button on them and also required power - the RCA jack doesn't have enough lines for that.

So, I'm going to suggest the second jack is for a second composite output. And indeed there does seem to be a second DAC (2N3904 transistor and some resistors) way over on the other side of the board. There is a third 2N3904 as well with some unpopulated resistors - not sure what that's for (a third, internal composite connector maybe?). I'm guessing this extra feature was added as a marketing point and because it was cheap and easy to do rather than because it was particularly useful, but perhaps some people had applications for driving multiple composite monitors from a single CGA card such as public information display screens in airports and railway stations.

The lower one is composite out, the upper one is connected to the feature connector, that's it. So yes, for a lightpen option, for example.

Thanks. I figured as much after looking over the card more closely last night, seemed to be connected to the light pen interface.

I haven't seen many CGA cards with both connectors on the back, glad at least one might be composite output.