Windows: press and hold Alt, then type 0209 for Ñ or 0241 for ñ on the numeric keypad
Mac: press Option + n, then press N for Ñ or n for ñ
iPhone/iPad: press and hold N, then select Ñ or ñ
Android: press and hold N, then select Ñ or ñ
Spanish keyboard: use the dedicated Ñ key
Copy and paste: Ñ ñ