Which is the correct angle (with the cable surface) at which the knife blade should be kept while stripping a cable?

Wire Stripping Steps Using a knife:

Generally, you will need at least 1 ½ - 4” or 4 - 10 cm of wire stripped off of the end, depending on the type of joint required.

1. Hold the knife close to your chest at a 30˚ angle (Between 20 and 45 deg) to the wire.
2. Thumb should be on the opposite side of the wire across from the knife.
3. Slightly pull a knife, while cutting to produce a slight saw movement.
4. Once through the insulation, your knife will glide over the conductor.
5. Cut away one strip of insulation, then rotate the wire, and continue until finished.
6. Aim insulation pieces down to the floor to maximize the safety of others around you.