Can’t find the ‘ñ’ in the special characters table.
⌥(option) + N, N → ñ
⌥(option) + N, ⇧(shift) + N → Ñ
To find the other interesting characters:
- activate the Keyboard Viewer:
System Preferences > Language & Text > Input Sources
Keyboard & Character Viewer
open the Keyboard Viewer, from the Keyboard selector within the menu bar,
press the ⌥(option) key (or any other keyboard modifier) to discover which character on the keyboard
may give you access to language specific characters (ex. : ⌥ + N → ã, ñ, õ, Ã, Ñ, Õ).
Note : this is not a shortcut specific to LibreOffice, you can use it within the Finder anf within any application.
Perhaps the specific font yo’re using doesn’t contain “Ñ”. The table in Insert > Special Character only shows the characters that the current font actually has, so try switching to another.
The code points should be U+00D1 (=209 decimal) for upper case and U+00F1 (=241 decimal) for lower case.