I have tried the following:
$ sudo killall -HUP mDNSResponder
$ sudo killall -9 mDNSResponderHelper mDNSResponder
$ sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist: Operation not permitted while System Integrity Protection is engaged
None of them stop mDNSResponder from running.
Why do I want to do this? I just want to stop it before closing the lid. Because this stupid app is waking up my system when my lid remains closed. I tried many ways to avoid it running when system is at sleep. But none of them works. So the best option is just to force kill it and re-run it later. Thanks a lot.
Btw, this is not a XY question. I mean I want to stop it. The above explanation is just to clarify the reason why I want to do it, otherwise, people may ask why I want to do it and ask me not to do. Well, I really want to stop it and this is the question. The app is 100% useless to me when my system is at sleep and my lid is closed. Thanks.