I pronounce it as though it were French: Sykes. Occasionally I'd pronounce it with a German influence: Sykes. Sometimes I feel a little Russian, and so I'd say: Sykes. I might even go out on a limb, use standard English pronounciation and say: Sykes.
I don't know every language, but considering it's obviously a basically western spelling with Nordic influences, I reckon you can feel safe if you follow your two previous followers and say:.....ready for it.......Sykes. ;)
I say it like sikes, or sigh ks
Either sigh- ks. or psychs