Thank you Werner ,
I've checked it before posting on forum.
The problem is Knoppix is not at the list of supported distros. I've took Debian 7 and the answer was:
You have selected Debian 7.0 using the HP LaserJet 1020 Printer.
Debian 7.0 supplies HPLIP 3.12.6 and it does support your printer.
As the version of HPLIP supplied with your operating system supports your printer, you may continue to use that version of HPLIP.

You may now optionally download the latest version of HPLIP to get access to new features and bug fixes.
I decided to reinstal HPLIP (or install it again) and after downloading the
hplip-3.13.6.run
file I start the install procedure and
error: debian-testing version is not supported, so all dependencies may not be installed. However trying to install using debian-7.0 version packages.
anyhow I've tried to continue automatic installation
Code:
Warning: There are 4 missing REQUIRED dependencies.
note: Installation of dependencies requires an active internet connection.
warning: Missing REQUIRED dependency: python-devel (Python devel - Python development files)
warning: Missing REQUIRED dependency: libusb (libusb - USB library)
warning: Missing REQUIRED dependency: cups-image (CUPS image - CUPS image development files)
warning: Missing REQUIRED dependency: libjpeg (libjpeg - JPEG library)


INSTALL MISSING OPTIONAL DEPENDENCIES
-------------------------------------
warning: There are 3 missing OPTIONAL dependencies.
note: Installation of dependencies requires an active internet connection.
warning: Missing REQUIRED dependency for option 'network': libnetsnmp-devel (libnetsnmp-devel - SNMP networking library development files)
warning: Missing REQUIRED dependency for option 'fax': dbus (DBus - Message bus system)
warning: Missing REQUIRED dependency for option 'scan': sane-devel (SANE - Scanning library development files)
for my internet connection is rather slow (I use GSM network) so it takes some time to install what is needed.
and at the end I've got :

Code:
RUNNING PRE-PACKAGE COMMANDS
----------------------------
su -c "dpkg --configure -a" (Pre-depend step 1)
su -c "apt-get install -f" (Pre-depend step 2)
su -c "apt-get update" (Pre-depend step 3)
warning: An error occurred running 'su -c "apt-get install --yes cupsys-bsd"'
su -c "apt-get install --yes cupsys-bsd" (Pre-depend step 4)
OK

DEPENDENCY AND CONFLICT RESOLUTION
----------------------------------
Running 'su -c "apt-get install --force-yes -y python-dev"'
Please wait, this may take several minutes...

error: Aborted.
I tried another time and
the installation note was:
"NOTE: Disable the CD Sources in your apt sources.list or the install will fail and hang."
this is why I've failed the first time.

And sorry for my ignorance but I don't know how to disable CD Source in apt , I'm not very familiar with console .

Anyhow I suspect that the message
There are 4 missing REQUIRED dependencies.
explains why I can not to force my printer to work in Knoppix.

Speaking frankly now I'm lost. I have no idea what to do now
I hoped to get some "how to" for there must be someone for whom this printer works
thanks in advance for any suggestions