Remove the given player or object (or, in the second form, everyone) from your 'gag list'. You will once again see any messages that result from actions initiated by the ungagged player(s) or objects. In particular, you will once again be able to hear them if they speak, emote, or whisper to you. See 'help gagging' for an explanation of gagging in general.
Example:
Munchkin types:
@ungag Grover
and is once again able to hear Grover's witty remarks. Sigh...