Using a web browser, navigate to your node's status page, and click on one of the links in My Shares. Then look for a section that looks like this:

(I recently switched my node over to btc1 too.)

The bitcoind version you're using (Unlimited/Core/btc1/etc) will include a version bits suggestion which gets passed to your p2pool node in the getblocktemplate response. Depending on which version of the p2pool code you're using, your p2pool node may either use the version bits it receives from bitcoind, or it may override it (see https://github.com/jtoomim/p2pool/blob/lowmem/p2pool/work.py#L386 for an example -- I've never liked that max() line, but haven't changed it in my branch yet). If you want to force particular version bits even though the bitcoind you're using doesn't make those version bits, you can do so by editing that line in your p2pool source code. Each p2pool node can use different version bits, so the final block version bits that you see depends on which p2pool node actually mined the block.