I find it amazing that there is a line tool, an Oval, and a Box, but no Curve in the Mobile app at all. Just the simple ability to set my anchor points, and then push/pull the curves "magnet" would be huge. The closest thing one has is to try to use the protractor ruler tool as a work around, but that is just so clumsy. I can accomplish in seconds at my Desk in ClipStudio what takes minutes in SketchBook Mobile on my Tablet; but I can't hardly carry my desktop out in the world. If one is trying to sketch something long smooth curves, like a Modern car its a frustration.
Lately I find while Sketchbook has a great many brushes I'm finding it rather shy of Tools. A Dynamic Curve tool would be great, even a French Curve tool would be a great help. The Oval Protractor that is all was have today is just not a substitute.