1 John 2:21
I did not write to you people because you are ignorant of the truth [about these matters], but because you do know it, and because nothing false belongs to the true teaching.
2 Peter 1:12
Therefore, I intend to constantly remind you people about these things [i.e., those mentioned in verses 5-11], even though you [already] know them, and have been established in the truth you now possess.
Romans 15:14-15
And I, myself, am convinced about you, my brothers, that you yourselves are full of goodness, and have been filled with all kinds of knowledge and are capable of counseling one another.
Jude 1:5
But, I want to remind you, [even] though you already know the stories about how the Lord delivered His people from Egyptian [bondage], and then [later] destroyed those who did not believe [in Him].