This tool is not yet available in ArcGIS Pro, and it is missed.
Using the Grid Index tool just isn't the same when creating map series of trails.
Amanda, make sure to up vote your idea. While it isn't a 1:1 match for now, Pro does offer the Generate Rectangles Along Lines—Data Management toolbox | ArcGIS Desktop tool which will probably get you most of the way unless you use some of the specific data driven page attribute fields from the ArcMap Strip Map Index Features tool.
Ideas in ArcGIS Pro 2.3
Retrieving data ...