How do you represent Ctrl-Space in a keytrigger?

KeyPressTriggers are for single typed characters only, not for characters with modifiers, etc. If you want to do keypresses with modifiers then you should handle the KeyTyping event or override the OnSyntaxEditorKeyTyping method in your SyntaxLanguage class.

Be sure that you cancel the default behavior for Ctrl+Space though because by default there is a command link set up to call the language's IntelliPromptCompleteWord method if the language's IntelliPromptMemberListSupported property returns true.