The word(s) "knew" appears 38 time(s) in 35 verse(s) in Quran in Abdullah Yusuf Ali translation.

(31) That ye believe in Allah and His Messenger, and that ye strive (your utmost) in the Cause of Allah, with your property and your persons: That will be best for you, if ye but knew!

(32) O ye who believe! When the call is proclaimed to prayer on Friday (the Day of Assembly), hasten earnestly to the Remembrance of Allah, and leave off business (and traffic): That is best for you if ye but knew!

(33) Such is the Punishment (in this life); but greater is the Punishment in the Hereafter,- if only they knew!

(34) "So He may forgive you your sins and give you respite for a stated Term: for when the Term given by Allah is accomplished, it cannot be put forward: if ye only knew."

(35) Taught man that which he knew not.