It is known that the sphere $ S^6$ admits an almost complex structure by identifying $S^6 $ with the space of unit purely imaginary Cayley numbers.
I would like to show that this almost complex structure is not integrable using the Nijenhuis tensor.
Can someone explain to me how vector fields look like in $S^6$ and how can we apply them in the Nijenhuis tensor?
I found something in Ballmann's book (Kahler manifolds) but I didn't understand it.