Matching to the general sound of 12 tone music, the second entry should be on the tritone imho
Isn't this like saying that the second entry of a tonal fugue should always enter in the dominant?
Yes, exactly
There is a 12 tone "fugue" (fugetto? small fugue) in the Variations pour piano by Jacques Hétu (French Canadian Composer) Variation 3 I believe is the fugue...