A Nasik (= pandiagonal & pantriagonal) 6x6x6 magic cube does not exist. Besides a simple result, you have to choose for a diagonal ór a pantriagonal 6x6x6 magic cube.
[Medjig method] I used the Medjig method three dimensional (3D) to construct a simple 6x6x6 magic cube.
[Shift method] I did not succeed in finding regular grids to construct a diagonal 6x6x6 magic cube. I believe regular grids to construct a diagonal magic cube of double odd order do not exist. See below an analysis of Walter Trump's diagonal 6x6x6 magic cube.
[Method of Luyendijk] Luckily I found regular grids to construct a pantriagonal 6x6x6 magic cube in the 6x6x6 magic cube of Luyendijk.