On a Deposit, I can see where the payment has been applied and navigate directly to the record (in this case a JE debited to the undeposited funds account). Is there a way to navigate the other direction? I'm looking at another JE that is marked as "Payment Applied" but can't for the life of me figure out the best way to identify the corresponding deposit.

Try create a saved search with the journal as the criteria and add a result column for applying transaction / applied to transaction.. (I can never remember which one so I try both 😃 )