Pick a publicly known Bitcoin entity (an exchange, a notable wallet, a public-figure address). Reverse-engineer as much as you can from on-chain data: estimated holdings, address clusters, frequent counterparties, deposit/withdrawal cadence. Produce a 1-2 page brief.
Use mempool.space, blockstream.info, or oxt.me as starting tools. For larger probes, install BlockSci or use Glassnode. The OFAC sanctioned-address list is a good practice target (you can publicly check what they did).