Witnessing nonseparability of bipartite quantum operations

•Generalization of the concept of entanglement witnesses for quantum states to quantum operations.•Another application of the Hahn-Banach theorem and the state-operator isomorphism.•Method presented utilizes a maximally entangled state as a resource.•Method presented provides advantage over corresponding protocol without the resource. We provide a method for witnessing nonseparability of quantum processes on shared systems, which uses the channel-state duality. The method uses a maximally entangled state as a resource. We show that using the resource provides significant advantage over the corresponding protocol for nonseparability detection without the resource.