gnome-characters software package provides character map application, you can install in your Debian 9 (Stretch) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install gnome-characters
gnome-characters is installed in your system.
Make ensure the gnome-characters package were installed using the commands given below,
$ sudo dpkg-query -l | grep gnome-characters *
You will get with gnome-characters package name, version, architecture and description in a table
| Distro | Debian 9 stretch |
| Section | GNOME |
| Package | gnome-characters |
| Version | 3.22.0-1 |
| Description | character map application |
| Sub Section | gnome |