How to create the scroll of a viola?
If you mean the S shaped cutouts in the body, then you need to either create a sketch on the front face of the body or create a work plane above the front face of the body. After you do that, draw a centerline going through the middle of the face parallel to the strings. This line is so you can just mirror the shape over to the other side instead of drawing it again.
After that, draw the scrolls using a mix of circles and arcs. Trim away the unneeded lines after you get the shape you want.
Next, click on the "mirror" icon in the toolbar. You can either click on the individual lines or you can highlight them all. Then go to the little window that pops up with the "mirror" action and click on the button to select the mirror line. This is where you select that mirror line that you drew earlier.
Click "Enter" and accept or whatever.
Right click and hit "Finish sketch"
Hit the extrude button and click on the scroll shapes, and then enter the depth that they need to be cut out. Hit "Enter" once you're happy with the results.
I hope this helped! if not, send me a personal message and I'll try helping you further.
The only thing I can think of doing is just leaving that basically one big chunk and carving it by hand, but that's because I am thinking like a machinist. I'm sorry, I don't know how to model that :( Maybe you can play around with the "Coil" function and see if it can taper, but I have no other ideas. Maybe you can just make a flat shape and then just use the spline function and make a spiral. From there, you can give the spline some thickness and cut in via extrusion, then chamfer it so it has a cinnamon roll sort of look to it.
I wish I knew how to do that! Now I have something to learn! Once I figure it out, I'll tell you how to do it!