My understanding is that the pub keys that are generated when sending to a subaddress are indistinguishable from other pub keys on the blockchain. In other words, if you find a transaction with greater than two outputs, though you'll know multiple addresses were sent to, you won't know whether either or both of them were subaddresses.
I previously answered that output pub keys were not distinguishable from one another in terms of whether they relate to subaddresses or not. This isn't necessarily relevant to the question, however.
You just want to literally be pointed to a transaction so you can see what it looks like when there are extra tx pub keys in tx
extra. I may delete my answer if I don't manage to find a transaction to point you to.