I'll be arriving in HKG from JFK on CX F, connecting to TPE in CX J 3 hours after arrival on a separate ticket. My friend will be joining me for the TPE flight in J, am I correct to assume I will get F access and be able to guest him in as well?
Unless the "no interlining" changes also imply a redefinition of "connecting between" then you will get access to the F lounge, yes.
Interesting question about the friend - I've never seen that question asked before.
If you are OW Emerald or were departing on F then the answer would clearly be yes to the guest. But in the case of access through incoming F then I see nothing in the CX or oneworld websites that covers it.