Is there a way to see what options a text layer has applied to it?
For example, how do I see if a text layer has an uppercase transform?
textLayer.styleAttributes()["MSAttributedStringTextTransformAttribute"] - null: none, 1: uppercase and 2: lowercase. You should be able to get the other options as other attributes in textLayer.styleAttributes().
Are these constants identified anywhere that is exposed?
Which constants are you referring to? If you're referring to uppercase, lowercase etc., no the enums are not exposed. If you are referring to the attribute keys e.g. "MSAttributedStringTextTransformAttribute" some of the Objective-C constants are listed here.
If I were trying to find out if the option to underline was applied to a text layer what would would I should I call to check?
I think I found my answer: https://sketchplugins.com/d/768-text-decoration-underline/3