How to project a point $x_0$ on an ellipsoid's surface and on its principal axes?

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Following Given 3 orthogonal vectors how to calculate the ellipsoid induced by them?

Assume an arbitrary point $x_0$ and an ellipsoid defined as $(x-v)^t A (x-v) = 1$

Where the ellipsoid's principal axis matrix is given by: $W = [w_1 | w_2 | w_3]$ s.t. $W^t W = I$.

  1. How to project $x_0$ on the ellipsoid surface?
  2. How to project $x_0$ on the ellipsoid's principal axes?