I'm not exactly sure what you're asking

When sats in a lightning channel are sent to another address, every node that forwards the payment recieves the routing fee that the node has set. The lower the routing fee, the better the chance of getting someone to route through you.

If your payment requires 2 or 3 nodes, then those 2 to 3 nodes get their fees, but your channel is direct with the node you're paying, you pay no fees at all.

I hope this answers your question

Had trouble understanding specifically as to what you are asking.

Are you referring to how you can do a post and then under Options choose to "forward sats to" another SN user? If so, that's not using their Lightning address, it's just an internal ledger transfer.

But I suspect it just shows up in notifications for them as if they had done the post themselves. I'm not sure though.

Or are you asking how, if someone receives a tip to their account on SN and that tip was sent using their Lightning address, how does that appear? There is a notification that sats have been deposited. There is no "memo" / "message", and SN can't know if that was a tip or you depositing that yourself.