Many web sites suggest to tap the very top of the screen (the status bar) but that does not work. It just shows the URL entry field and the tab "ears". I also tried double tapping. Nothing seems to work.
I have iOS 12.1.1
(I'm also interested in a solution for iPhone. There the "tap the status bar" seems to work sometimes, but many times it does not)
Best Answer
Tapping the status bar is the system-wide scroll to top.
If the location bar in Safari is collapsed, the first tap anywhere in that area is overridden to expand the bar. If this happens on the first tap, now tap the status bar area.
The tap to scroll to the top only works when the location bar is expanded. This applies to iPhone and iPad alike.