what do you do when you don't know the topic for debate and you're 3rd speaker and you have to talk for 6mins?

Generally in debates, you don't find out the topic until an hour beforehand.

Third speaker is actually an easy position - the easiest of the three active speakers (fourth speaker doesn't count :P). Basically, you should:

1. Rebut the last speaker from the opposing team - work with your team's fourth speaker (it's his job to help with rebuttals)

2. Repeat the teamline/mainline

3. Sum up the arguments put forth by the first and second speakers (including any particularly strong points from their rebuttals)

4. Close the debate for your team on a strong note.

The third speaker should never introduce new content or arguments to a debate, merely revise what his teammates have said.

take prep time and ask ur teams wut they were saying in general and kind of explain that