All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
Knowledge in Islamic terminology means the knowledge of the Quran and the narrations of the Prophet whether it is related to Islamic creed of Fiqh.
Islamic knowledge means learning the teachings and commands of Allaah and His Prophet . So, the knowledge of creed is a religious knowledge, its rank is very high compared to the knowledge of other religious fields. Knowledge of Fiqh is also religious knowledge through which a Muslim learns how to worship his Lord. A person cannot be a religious scholar unless he acquires the knowledge of the Quran and the Prophetic narration whether it is related to creed or Fiqh.
To know the teachings and commands of Allaah one has to learn those sciences like Usool Al-Fiqh, Arabic language with all its branches and the like.
As for the knowledge that is "devoid of faith", if you mean worldly sciences like medicine, engineering, and the like, then they are useful; learning them is a communal obligation on the Muslim nation since they are in need of it. So, whoever gains such knowledge with the intention of benefiting the Muslim nation will be rewarded.
Imaam Ibn Al-Qayyim wrote: ' … For this reason, a group of the Hanbali and Al-Shaafi'ee scholars say that learning these professions is a communal obligation since the people need it.'
Allaah Knows best.