I doubt FOTAQ was coded in AMOS, more likely it's coded in C and use some SCUMM-like (Lucas' scripting language for Adventure games) script language (if not SCUMM).
Anyway when a program is compiled into a binary file (executable) there's no way to get the source code back in the language it was written with. All you can see if the ASM code (wich won't help you too much if you are a newbie and code only in Basic).
To create point and click adventure game I think there is some software that allow you to create this kind of games without much programming knowledge. I've seen some on Windows but I'm pretty sure there was also on Amiga. I don't know what they worth tho. You may also want to look at BlitzBasic or why not Flash...