There were windows on the command module to look in, and if they weren't sure if he was responsive/unresponsive, they could tap iron onto the command module to let Collins know they were there and spacewalking.
It's an interesting thought process though, and I would appreciate the source if you can find it
https://spaceflightblunders.wordpress.com/2017/04/07/lunar-o...
From the article, I was wrong about not knowing whether the CMP was alive:
"Unless there was a very serious issue with the CM’s communications systems, NASA would know of the CMP’s fate immediately. Every astronaut wears biomedical sensors at all times, as part of their constant-wear garment. This telemetry is sent to the flight surgeon."
More discussion here:
https://space.stackexchange.com/questions/45426/procedure-to...
A comment from that page:
"Probably the worst scenario would be for the CMP to be alive, but disabled and not in his spacesuit. There would be no way for the other astronauts to get to the CMP without depressurizing the CM, thus killing the CMP. It's an obvious choice between three astronauts stranded in lunar orbit, versus two getting home alive. Nonetheless, I can only imagine the regret that the astronaut who would have to depressurize the CM would have."
So it is even worse than the way I remembered it: the LM pilots would likely know that the CMP pilot was alive but incapacitated and they were about to kill him.
https://www.newscientist.com/article/mg20627561-700-maxed-ou...
https://www.nasa.gov/audience/foreducators/spacesuits/facts/...
Edit: This says it can actually be done in five minutes in an emergency if one's willing to skip every safety check, but getting an unresponsive person into one seems like surely it would be more of a challenge -- particularly if the "helper" was wearing a spacesuit himself. Those things are awfully restrictive! And I would wager it's not a scenario they practiced.
https://airandspace.si.edu/stories/editorial/how-do-you-put-...
I've been in a number of situations myself where swift incapacitation would have killed me. This is common.
