# I will not keep silent concerning ... nor about ... nor about
This can be translated in positive form. Alternate translation: "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.