He knew of every jutsu in Konoha, that's why he was called the professor; like teachers, professors have extensive knowledge on a subject. But like Sasuke knows of Bijudama Rasenshuriken, he still can't use it.
OT:
Hashirama (Nature-based Ninjutsu, Kuchiyose, Bukijutsu, Genjutsu, Sensing, Medical Ninjutsu, Fuinjutsu, Senjutsu)
Tobirama (Nature-based Ninjutsu, Somatic Ninjutsu*, Kenjutsu, Kinjutsu, Sensing, Bukijutsu, Kuchiyose)
Kakashi (Nature-based Ninjutsu, Somatic Ninjutsu, Bukijutsu, Genjutsu, Fuinjutsu, Kenjutsu, Kuchiyose, Taijutsu speciality**)
Jiraiya (Nature-based Ninjutsu, Somatic Ninjutsu, Genjutsu, Fuinjutsu, Kuchiyose, Senjutsu, Kekkei Ninjutsu, Fuinjutsu)
Itachi (Nature-based Ninjutsu, Somatic Ninjutsu, Genjutsu, Fuinjutsu, Kuchiyose, Kenjutsu, Bukijutsu)
*Somatic Ninjutsu refers to techs that aren't nature-based, e.g. FTG, Kage Bunshin no Jutsu and Rasengan
** Taijutsu speciality refers to his ability to open at least one of the Eight Gates