"Sapere" generally means to have knowledge (~ to know) but in passato prossimo the meaning changes towards had gained knowledge had learned / had heard / had found out.
Find out more at ThoughCo
Aveva saputo = (he/she/it) had found out/heard/learned
troppo = too much
He/she had found out too much.
Trapassato prossimo di Sapere (had found out):
According to these articles the meaning of sapere changes in the passato prossimo to "found out" but this does not apply in the other tenses.
doveva essere strofinato? was he the genie of the lamp? :P
just kidding... maybe you wanted to say "doveva essere fatto fuori" (eliminated)
"strofinare" is just the literal translation of rub: you can strofinare a rubber on the paper, or a sponge on a plate etc. but "strofinare fuori" doesn't have any sense for me.