Yup I had same error with Vapor and fixed it, but this is swift-jupyter fix, please see details here.
Let me check SwiftSox, maybe it has different problem, though.
UPD: Yes, it works with this swift-juputer fix. I can import SwiftSox and call InitSox() w/o error (had to make it public, though 
) Try patching your swift_kernel.py with my fix as a temporary workaround?