How can I get logging information on incoming transactions with bitcoind?
If you run the daemon or the GUI (bitcoin-qt) using the debug=1 argument, then bitcoin will write a variety of events to the debug.log file, including info about transactions received by your node.  

I just ran a test to confirm this. You could follow these steps if you want:

(1) From the terminal window, start bitcoin-qt like this: $bitcoin-qt -debug=1

(2) Navigate to the /.bitcoin folder: $cd .bitcoin

(3) View the last few recent entries into the debug.log file: $tail debug.log

When I did this, I saw the following entry:

2017-11-21 12:58:54 AcceptToMemoryPool: peer=3: accepted 4e1a7429f28c7410e177bf3278aca76b6e32e097ed8d87dbd18980de9c23f343 (poolsz 18765 txn, 94644 kB)


I then copied the transaction ID and cross-referenced it at blockchain.info:

https://blockchain.info/tx/4e1a7429f28c7410e177bf3278aca76b6e32e097ed8d87dbd18980de9c23f343


And as expected, it was there as an Unconfirmed Transaction (which makes sense because the log entry mentions "AcceptToMemoryPool", so it sound like my node received a transaction from a peer, and has decided to put it in the mempool - that's just my guess, maybe I'm wrong)