The brushes on Android/iOS (Mobile) do not transfer over to the Desktop version of SketchBook.
The brushes on the "Mobile" versions of SketchBook cannot be exported or imported into another version of SketchBook on a different device.
http://help.autodesk.com/view/SKETPRO/ENU/?guid=SKETPRO_Help_sb_brushes_export_brush_sets_html
I would log a suggestion here:
https://forums.autodesk.com/t5/sketchbook-ideas/idb-p/804
or up-vote this one:
https://forums.autodesk.com/t5/sketchbook-ideas/import-brushes-to-mobile/idi-p/8768372
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