Choose a recently announced or completed transaction with enough public information to research. Merger and acquisition deals are often easiest because you can discuss the buyer, target, strategic rationale, valuation, financing, and risks. An initial public offering or debt issuance can also work if you understand the relevant market dynamics.
Prioritize understanding over prestige. The largest deal in the news is not automatically the best choice. A smaller transaction in an industry you follow may produce a much better conversation, especially if you can connect it to sector trends or explain why it interested you personally.