I hope this makes sense because I am not really good with vectors. But imagine I have two $3$-dimensional position vectors at points $A(2i + 3j + 3k)$ and $B(5i + j + 4k)$. Then imagine a straight line $c$ goes from point $A$ to point $B$ then I use the line $c$ to form the hypotenuse of a right angle triangle. How can I measure the angle in the triangle?
Remember this is is all in $3$D.
The vector from A to B is AB = B-A = (3i -2j + k). So you know 3 vectors OA, OB and AB. You can find the angle $\theta$ between any two vectors using the dot product formula $$X.Y=|X||Y|\cos(\theta)$$ so $$\theta=\cos^{-1}\left(\frac{X.Y}{|X||Y|}\right)$$ However, I am not clear where the third vertex in your right angled triangle is. No pair of vectors from the vectors you have is at right angles to one another, otherwise their dot product would be 0.