Just to paste in the wording from their IK FAQ:
Q: Weapons on Walkers are listed as being fixed forward, and the rules for Super-heavy Walkers say that they follow the shooting rules for Walkers. Does this mean that all weapons on an Imperial Knight are limited to the 45° front arc, even including their arms which can physically move much more than 45°, and their carapace weapon which can physically rotate 360°?
A: Treat the Imperial Knight’s arm-mounted ranged weapons as sponson-mounted weapons (see Warhammer 40,000: The Rules) for the purposes of establishing their line of sight. All Imperial Knight carapace weapons have a 360° line of sight.