#1: Pull-down: Grab his knife hand and wrist.
Pull it down from your neck & against your chest. Do NOT pull it away from you. [OK] Weakness: If the attacker is significantly stronger than you this won’t work.
#2 Push: Hit or push his arm [at elbow] in direction of the knife.
Be sure to turn your head away from the knife & hold his arm in place as you continue. [Better] Weakness: You’re not effectively controlling the weapon at this point.
#3: Push-Pull: Grab his right wrist with your left hand & push his right elbow as in #2 above.
Turn your head away from the knife as you pull down with your left hand. Hold his arm and knife hand tight against your body to restrict movement. [Much better than #2] Weakness: Not much except as you execute any type of technique you still have to be very much aware of the knife. Good follow throughs include drop throws [otoshi].
#4 Push-Slide: Bring your right hand up to strike his right upper arm at the elbow.
As you push his arm across, turning your head away from the knife, your left hand starts to slide up under his forearm, palm facing you.
Continue upward slide of your left hand as you finish pushing his arm. Keep your hand against your face as you do this counter. [BEST] Weakness: The back of your left hand or forearm could be cut if he can slide back, but your face & neck are relatively well-protected. It’s easy to go into a shoulderlock rear takedown [ude guruma ushiro] from this point.