Here you can find all necessary information to use tooltips in your application.
Firstly, add the following files:
<script src='../../codebase/ext/dhtmlxscheduler_tooltip.js' type="text/javascript" charset="utf-8"></script>
dhtmlXTooltip.config.className = 'dhtmlXTooltip tooltip';
dhtmlXTooltip.config.timeout_to_display = 50;
dhtmlXTooltip.config.delta_x = 10;
dhtmlXTooltip.config.delta_x = 60;
scheduler.templates.tooltip_text = function(start,end,event) { return "<b>Event:</b> "+event.text+"<br/><b>Start date:</b> "+scheduler.templates.tooltip_date_format(start)+"<br/><b>End date:</b> "+scheduler.templates.tooltip_date_format(end); }
scheduler.templates.tooltip_date_format=scheduler.date.date_to_str("%Y-%m-%d %H:%i");