White has got a warrior on the magic square k9. This can move k9 – k10 x, opening a route for the king which will be unstoppable (black’s only move is i11 – j11, which is countered by i10 – i11 x)
White has another winning position at the bottom right corner, thanks to a warrior on magic square i1. The king must move j6 – j3 first, and then nothing can stop the following move i1 – j1 x, and the king is unstoppable. (If black moves j2 – j1 x which captures the white warrior on i1, then white replies by moving the king forward j3 – j2, and he is then on an open file and unstoppable again.)
Incidentally, notice that the king is on the second rank, not the third – this is an excellent place for him to be, to exploit the white warriors’ positions on the ends of the third ranks. Try it out on your hnefatafl board, and then try it with the king on i6 (third rank) instead of j6. You’ll find black can block him easily. If he were on k6, that would be good, as k9 – j9 opens up the k-file and if black blocks with j10 – k10, the king can just capture it with k6 – k9 x.