First try to place this code into the "Remote" tab in Script Editor into a new file.

Code:
ON *:CONNECT: {
  raw CAP REQ :twitch.tv/membership 
  raw CAP REQ :twitch.tv/commands 
  raw CAP REQ :twitch.tv/tags  
}


Then in order to view the nicklist when you connect into the server and join into the channel from the channel tabs (switchbar) use right click into the channel and select 'Nicklist' then select the 'right' option from the dropdown box and press 'OK' , check the images below.





Make sure you are using the latest mIRC version (7.43).

Need Online mIRC help or an mIRC Scripting Freelancer? -> https://irc.chathub.org <-