Light up a cigar and and have another astronaut float around outside and see the smoke blow out.
hehe...I was thinking use a vaping thing...but the exact same idea.
Some CO2 might work too, but you would have to have an idea where it might be located first. Or some other harmless gas with a bit of coloring in it. Ozone or Argon maybe? But again, you’d have to have a clue where to look. Both are basically harmless in small amounts. Argon is used in TIG and wire welding.