It's a challenge to mate with the three knights without other white pieces to lose a tempo, but not to worry it should be possible in ten moves: 1. Nf4 Kg8 2. Nd3 Kf8 3. Ne5 Ke8 4. Ngf7 Kf8 5. N7d6 Kg8 6. Ng6 Kh7 7. Nge7 Kh8 8. Ne4/Ne8 Kh7 9. Nf6+ Kh8 10. Ng6#