Option 1 -> "had saw" is grammatically incorrect; the past participle of "see" is "seen," not "saw." Also, "spoken" is incomplete without the auxiliary verb.
Option 2 -> Correctly uses the third conditional structure (If + past perfect, would have + past participle) to express an unreal past situation.
Option 3 -> "Seen" without "had" is incomplete, and "would speak" is second conditional (present/future), not appropriate for a past situation.
Option 4 -> "had see" is incorrect (should be "had seen"), and "would have speak" is incorrect (should be "would have spoken").
Hence, Option 2: had seen, would have spoken -> This is a third conditional sentence expressing a hypothetical situation in the past that didn't actually happen. The speaker is saying that if they HAD seen the person at the party (but they didn't), they WOULD HAVE spoken to them (but they couldn't because they didn't see them). -> correct