Look at your Windows character map to find the key combination you have to type to get them. it will be the hold the alt key with a four digit number, like alt-0174 gives this: ®
Ligatures that are a distinct letter such as Æ, æ, Œ, œ and ß sometimes have alt codes. Stylistic ligatures like ff, fi, fl, ffi, ffl, ſt, and st usually do not. But you can copy and paste most standardized ligatures from Windows Character Map. Some fonts may contain non-standard ligatures, which I don't think will show up in Windows Character Map, but they will show up in the glyphs panel in Illustrator (Signlab might have something similar?)