How do I send compass app data to apple watch?
There's currently no way to get data from the iPhone's Compass app to your Apple Watch, and no complication option available. There is no API on watchOS for compass heading and you would need to have your iPhone / iPad out and pointing in a specific location for the watch to match the iOS device.

I suppose you could mount the phone to a stand inside a ship or vehicle and know that the watch is showing where the other device is pointing and not necessarily where your watch is "pointing"


https://developer.apple.com/documentation/corelocation/getting_heading_and_course_information


This sort of "making do with what's available" is documented here in open source as well as dozens of App Store apps where no one in particular stands out as good or useful to me.


https://github.com/woutercx/iOS.Compass.Sample


You would have to adapt that for watchOS complication and iOS companion app. 
In the Watch app on your iPhone you'll find an App Store icon on the bottom that allows you to search for Apple Watch apps directly. You'll find there's a number of Compass apps available you can try doing exactly what the code above allows and no more or no less.

There isn't a magnetometer in the watch so it doesn't get it's own magnet in early 2019 at least.