I think of this knot as 'cowboy drape', rather than 'knot', as it seems so much more to do with arranging the folds than knotting.
Fold your scarf into a triangle
then fold the long edge over
gather the ends together
and bring behind your neck
cross the ends..
.. and bring them forward
From here, you can secure the ends with the basic slide, or the criss-cross method. For the basic slide click here, and for the criss-cross here