There's no system action for that for GJ Wall. There is for comments on an activity entry if using CB Activity and the relevant system actions to integrate with GJ. I recommend no longer using GJ Wall, GJ Photos, GJ Videos, and GJ Files and instead use the CB Activity and CB Gallery system actions that integration streams and galleries into GJ; those GJ integrations are on maintenance mode only now and will only get bug fixes as they will be removed in the future when CB Activity and CB Gallery integrations are just built into core GJ.