You license your contributions under an open licence. You don't give up your copyright. There would be no other sensible way to operate a collaborative encyclopedia without a license of this kind.
I (lawyer) have never encountered a jurisdiction where a contractor could not license their work under the contract with their employer (the person contracting them).
I (lawyer) have never encountered a jurisdiction where a contractor could not license their work under the contract with their employer (the person contracting them).