I trying porting silverlight/xna-game to ios, but doesnt know how I should make GUI. Do I have to use only Monogame or can I use something external gui-libraries? And if I have to use only Monogame, is there any Monogame-based gui-library what working on ios?
You can try Empty Key UI - http://emptykeys.com . It’s very close to release. Library is Portable Class Library profile 259, which is pretty much compatible with Xamarin. If you have any problem, let me know on forums.