Mike Rogers first met with Donald Trump in November of 2016, while Rod Rosenstein was appointed to his current position at the end of April 2017... hopefully the president was brought fully up to speed on RR by then in spite of the advice/assistance of GOP-e imbeds (past and present).
Probably sooner. I'm sure Sessions isn't quite the bump on a log he's usually portrayed as. He was in DOJ as a USA before being elected to the Senate. He likely had informed opinions on many people, especially as how to staff DOJ had to be on his mind. I suspect he (Sessions) had a reasonable handle on RR in January, before RR was nominated.
Other than for curiosity, it doesn't matter if Trump or Sessions or both were of a mind that RR would be a skunk; or if they were uncertain (In January/April 2017) and decided to risk a chance. The important thing is they were prepared for a "bad outcome" on that front.
Anyway, agreeing with you that Trump was as up to speed as one could be, in spite of all efforts to derail his presidency and his agenda. In an operation like FedGov, it is inevitable that certain forces will work subtle sabotage and subversion. It isn't like a business where success is measured in profit and customer satisfaction.
Trump first mentioned wiretapping March of 2017.
I still assert that he was not told until after he was President elect and he was legally allowed to be given that info about the FISA warrants.