Could not initialize GTK! Is DISPLAY env var/xhost set? on Debian WSL

I'm trying to use a file "testar.sh" to test GHDL and GTKWave installation on Debian, that's the command I should use: chmod +x testar.sh; ./testar.sh, then this is what its shown

Could not initialize GTK! Is DISPLAY env var/xhost set?
Usage: gtkwave [OPTION]... [DUMPFILE] [SAVEFILE] [RCFILE]

and a list of commands

I had a similar issue, when I tried to run gtkwave in windows subsystem for linux (WSL) with ubuntu distribution. The error is due to not having a X server for windows.

My solution was to download Xming. Then, with Xming running in the background, run export DISPLAY=:0 and you should be able to run your commands that require an X server.

See more info here