Do we have to send again a fresh QuoteRequest after re-login?
This answer is counterparty-specific. The FIX protocol does not answer this. You really need to ask your counterparty. My gut says that the answer is probably "yes", but you should confirm with them.
FIX gives a default set of application-level messages and fields, but does not describe how they must be used. Therefore, every counterparty does things a little differently.
or de we have to send a ResendRequest?
Heavens, no! ResendRequest is a transport-layer message; the QF/j engine will send this automatically when it's needed. You should not send it manually (just like you shouldn't send a Heartbeat manually).