3 Variations:

a) The UX Dept Receives the Approval document

1. UX attaches the approval to the Wireframe Approval task and @mentions the project Manager 
2. UX completes the task and move forward

b) Project Manager Receives the Approval document

1. The Project Manager attaches the approval to the Wireframe Approval task
2. Project Manager @Mentions UX dept notifying of the approval being received
3. UX completes the task

c) Both PM & UX Dept Receive the Approval document

1. UX attaches the Approval to the Wireframe Approval task and @mentions the Project Manager
2. UX completes the task

Below is the example of attaching the Wireframe Approval Document and @mentions UX on Wrike. Note that UX is the only one who can complete the task.