Across 1,557 ranked games on patch 16.21 in Master and above, Kha'Zix mains win 53.1% of their games in the jungle.
Their most common build appears in 40.5% of those games and wins 52.3% of its 631 games.
It starts 
Scorchclaw Pup, completes 
Umbral Glaive, 
Voltaic Cyclosword, 
Edge of Night and 
Serylda's Grudge in that order, and takes 
Ionian Boots of Lucidity.
Two other builds are played often enough in the jungle to be measured on their own.
In the jungle, Kha'Zix mains fare best against 
Viego (won 82.1% of 28 games), 
Bel'Veth (won 83.3% of 12 games) and 
Evelynn (won 76.5% of 17 games).
Their hardest matchups, the champions that counter Kha'Zix, are 
Rek'Sai (won 34.8% of 23 games), 
Zyra (won 30.8% of 13 games) and 
Cho'Gath (won 39.1% of 23 games).