Non-participating: at liquidation, an investor chooses. They may either be paid back their investment (or more, if they have a multiple), OR they may choose to convert to common and get that percentage. They will, obviously, choose whichever pays them more =P
Participating is then also obvious: investors get their money (or negotiated multiple) out, and then get their ownership percentage of the remainder.
One thing that happens is companies very eager to raise monster rounds agree to shitty terms on all of the above. It's a lever founders and investors can manipulate to raise bigger rounds.
see eg https://medium.com/@CharlesYu/the-ultimate-guide-to-liquidat...
So your answer: $28m. Because if you agreed to 2x preferences, you're raising on shit terms and the investor probably got participation as well.
Generally if you raise on good terms, you can get a 1x non-participating.
But it's good to know the details.
If the company sells for $100M, the investor gets $20M off the top. My question: Does the investor still own 10% of the shares, and will they recoup $8M of the remaining $80M?
Is their $10M investment now worth $20M or $28M?