Lv.24
he learns slash on level 42.
The move slash is learned at level 38.Hope this helps.
It learns slash at level 28 I think
Sand-slash learns dig at level 35 because i have one and it learned dig but you can teach him the TM dig too. Hope i helped ummm mine is level 35 and hasn't learned dig yet you sure its 35? he does not learn dig at lv.35
Crobat learns air slash at level 51
Tranquill learns air slash at level 32
Level 31
it learns it when its caught
In Pokémon Diamond, Gabite will need to go to the Move Remember's in the order of not knowing Tackle, Sand-attack, Dragon Rage, Sandstorm, Take Down or Sand Tomb however it'll learn Slash at Level 28, Dragon Claw at Level 33, Dig at Level 40 and Dragon Rush at Level 49. Garchomp will need to go to the Move Remember in the event of not knowing Tackle, Fire Fang, Sand Attack, Sandstorm, Dragon Rage, Sand Tomb, Take Down, Slash, Dragon Claw and Dig however it will learn Crunch at Level 48 and it will alsao learn Dragon Rush at Level 55.
Sceptile, to my knowledge, is incapable of learning Night Slash.
At level 80 it learn Aqua Tail and at level 90 Aura Sphere.
It learns air slash at level 62 on the 4th generation games