Mint from a live boot should pop a notification window in the top right to tell you you have no connection. Fades out.
Else, there will be a broken connection icon bottom right - click that to get a list of available connection points.
(applies for either Cinnamon or Mate)
Probably depends on driver being present as mentioned above.
used to be true, up to 17.3; haven't actually booted Mint18 live ...