You can specify the event bubble content using "bubbleHtml" property. Assigning new DayPilot.Bubble() to dp.bubble is not necessary (it uses an empty Bubble object by default).
Example:
dp.events.list = [
{
id: 1,
bubbleHtml: "Event details...",
// ...
}
];
The "html" property is used for the event box content (it overrides the "text" property if specified).
See also:
https://api.daypilot.org/daypilot-event-data/
Let me know if it didn't help.