Use the .deb package from http://www.kde-apps.org/content/show.php/kajongg?content=103206. If it does not work for you, you can download kajongg-x-y.tar.gz from the same address and then do:
tar xfz kajongg-x-y.tar.gz cd kajongg-x-y ./setup.py install
In both cases you will manually have to make sure that some other required packages are installed. The debian package does not yet contain these requirements. Kajongg needs: (corresponding debian packages in parentheses)
the KDE4 games library (libkdegames5)
Python 2.6 or higher (python)
QT4.4 or higher (libqt4-core, libqt4-gui, libqt4-svg, libqt4-sql, libqt4-sql-sqlite)
the python bindings for QT4 (python-qt4, python-qt4-sql)
the python bindings for KDE4 (python-kde4)
the python twisted library (python-twisted-core)
sqlite3 (libsqlite3-0)