Methods to make autocomplete work in Monodevelop-
- Method 1 -
Go to Unity > Edit > Preferences > External Tools > External Script Editor and than change form MonoDevelop(Built in) to manually browsing to MonoDevelop install location. Generally in PC the monodevelop install location is "C:\Program Files (x86)\Unity\MonoDevelop\bin\MonoDevelop.exe". Below that, also check the option of Add .unityproj's to .snl. Just click okay and restart Unity and check if autocomplete in monodevelelop is working, if not try the following.
- Method 2 -
If you have just started working in Unity and MonoDevelop that this method is more likely to work for you. You need to enable .NET Framework 3.5, it includes .NET 2.0 and 3.0. To enable just go to control panel > program and features then select turn windows feature on or off and then scroll down to .NET 3.5 and enable it.