Both of your versions are ungrammatical, I think.
That is because you are saying "is discussed". If the meeting is going on at the time when this phrase is being said, then you should have "that is being discussed in a meeting". Also, it seems that the "meeting" is a specific or definite event in this case, and therefore it should take "the"; if its a specific proposal you are talking about you should use "the".
1(a)."This is the proposal that was discussed in the meeting [earlier today/yesterday], and a vote was taken on it."
This is the first version. I changed the tense to fit "discussed". In the second independent clause, "it" is referring to the "proposal". Note the use of comma.
This one works too (different tense of the same version):
1(b)."This is the proposal that is being discussed in the meeting [right now], and a vote will be taken on it [by the end of the meeting]."
On to the second version now (the one you suggested):
"a proposal that is discussed in a meeting and on which a vote is taken"
This has the same problem as before. If you change the articles, and phrase it like the first rephrased version, it should look like this:
2."This is the proposal that was discussed in the meeting [earlier today/yesterday] and on which a vote was taken."
This is fine too. Note the comma is no longer needed here.