DNA with different chirality (would likely prove distinct origins better than genetic overlap, if life was seeded from the same origin billions of years ago there could be no overlap today, and some overlap doesn't prove origin either since gene can develop independently even very specific mutations), proto-life - RNA world/self replicating proteins...

Both of those would likely be a "more interesting" thing to study.

The most boring part would likely be finding DNA life which is quite similar, I'm not sure it would point to any specific origin and if it's metabolically going to be quite similar to some life we can find on earth the overall new science from it might be fairly limited.