Proxmark's "auto" command should get you most of the way to knowing.
Then check if any of the "hf mf c*" commands work on it (in which case, you have a gen1a magic card)
Nice, I didn't know about auto, thanks! It turns out I have some Gen 1a "magic" cards (as in, actually in a card form factor), and some tags that seem to be Gen 3, but not magic?
Gen 1, 1a, 3 and 4 all use special commands to unlock and edit block 0.
Gen 2 treats block 0 as always being r/w. This allows Android phones to directly write to it (but also makes it possible to lock the card).
In terms of pm3 commands, "auto" tries everything. You might also want to use "lf search" or "hf search" to only try one of your antennas and not the other.
The actual Magic part isn't really important here, since my phone doesn't even care about block 0. It just makes it easier to read and wipe the card when you have the extra command set at your disposal.