View source for Enable password feedback when entering sudo password

You need to add pwfeedback to the sudo defaults, there are two ways to do it, the latter is probably better

=== By editing /etc/sudoers ===
Run visudo (allows editing sudo config safely)
 sido visudo

Find 'Defaults' section:
 Defaults env_reset

Add pwfeedback to 'Defaults'
 Defaults env_reset,pwfeedback

=== By adding a special sudoers.d custom rule file ===
Alternatively you can also add the following file
 /etc/sudoers.d/enable-pwfeedback
Containing this string:
 Defaults pwfeedback