When traveling, Google Calendar will prompt to ask if you want to "Change time zone to ____?" One of the options is to "Never ask again". If you click the link to "Never ask again", there is no way within the Google Calendar UI to ever bring the link back.
In order to bring the link back, you can open Google Calendar in Chrome, type Cmd+Opt+J, paste the following code into the Console, and hit enter.
var xhr = new XMLHttpRequest;
xhr.open('POST', 'https://calendar.google.com/calendar/user_prefs');
xhr.setRequestHeader("Content-type", "application/x-www-form-urlencoded;charset=utf-8");
xhr.onreadystatechange = function() {