Personally, I wouldn't bother with a /whois for this, but rather use /ison or the /notify command.

For a single nick, the notify code is the one I would recommend, as it is the shortest.
For multiple nicks, I would recommend the /ison as most networks allow up to 16 nicks to be sent at one time with the /ison command.

I would only recommend the /whois code (with modification) if you wanted to join a channel that the person you /whoised was already on.

So you have code for your actual request, as well as 2 other options for you to consider.

For /ison
Code:
on *:connect:{
  if SquatNet isin $network {    .ison juicer  }
}
on *:snotice:ison*:{
  if $istok($2-,juicer,32) {    .join #channel  }
}


For notify
Code:
on *:connect:{
  if SquatNet isin $network && $notify(juicer).ison {    .join #channel  }
}


For /whois
Code:
on *:connect:{
  if SquatNet isin $network {
    .enable juicer_on
    .whois juicer
  }
}
#juicer_on off
raw 317:*:{
  if $2 == juicer {    set %juicer $true  }
  halt
}
raw 318:*:{
  .disable #juicer_on
  if %juicer {    .join #channel  }
  haltdef
}
#juicer_on end