Which sentence uses the best verb mood to persuade readers?

this lecture could be fascinating, so you should go, because it might sell out.
this lecture will be fascinating, so get your tickets before they disappear!

Your question is incomplete because have not provided all the answer options, which are:

This lecture could be fascinating, so you should go, because it might sell out.

This lecture will be fascinating, so get your tickets before they disappear!

This lecture would be fascinating if you went and listened, so go buy a ticket.

Do you think the lecture will be fascinating, and would you like to buy a ticket?

This lecture will be fascinating, so get your tickets before they disappear!

Explanation:

The imperative mood, used to give commands and requests, can cause readers to do something through induction and effort to convince. Besides, the use of Future Simple will suggests the promise or affirmation that the speaker or writer is talking about an interesting lecture.

The rest of the options are incorrect because they are written in the subjunctive mood and contain modal verbs of possibility and advice. As a result, they make reference to unreal situations, which do not encourage readers to buy tickets for an appealing event.