# I will not keep silent concerning ... nor about ... nor about

This can be translated in positive form. AT: "I will certainly speak about ... and about ... and about" (See: [[rc://en/ta/man/translate/figs-litotes]])

# concerning Leviathan's legs, nor about the matter of his strength, nor about his graceful form

These are three things about which God will not keep silent. 

# his

The word "his" refers to Leviathan.