You didn't specify what size but most dirt bikes will run a gap of 0.5-0.6 mm.
Impossible to answer, depends on what model KTM you have.
NGK Spark Plug BR8ECM
0.7 mm
NGK CR8EK or NGK CR8EiX (Iridium)
NGK CR9EKB 05 NGK CR9EKB 05
bad plug bad plug cap stator
I have a 07 KTM 525 XCW and the manual call for 6mm on plug gap.
br10ecmix
0.60mm
NGK BR8ECM
We use the nkg br9eix
NGK BR8HS with a .032" (0.8mm) gap