The command "/wl who <channel>" does not work correctly. Regardless from what I use for <channel>, the addon alway acts like if I had omitted the channel. The problem seems to be the following part of the function executed on waitlist's slashcommand:

local command, arg = strsplit(" ", strlower(msg), 2)
...
elseif command == L["command_who"] then
    chatmsg = listnames()
    if command == L["report_officer"] and GetNumGuildMembers() ~= 0 then
        channel = "OFFICER"
    elseif command == L["report_guild"] and GetNumGuildMembers() ~= 0 then
        channel = "GUILD"
    elseif command == L["report_raid"] and GetNumRaidMembers() ~= 0 then
        channel = "RAID"
    elseif command == L["report_party"] and GetNumPartyMembers() ~= 0 then
        channel = "PARTY"
    elseif command == L["report_say"] then
        channel = "SAY"
    else
        print(chatmsg)
    end

For "/wl who <channel>" command is equal to "who", arg will contain the channel. So the inner if should check arg and not command.