Assuming you really want and can travel that much in such a short time:
Mediterranean weather is relatively simple - dry and hot in summer, cold and wet in winter. For the trip in Italy expect rain and temperatures just above freezing to at best lower 10°C – extreme values can be slightly below freezing but hardly more than 15°C
For Switzerland, temperatures more or less around freezing, ofter colder by sunny weather (NE winds). For Jungfraujoch - assuming you mean Jungfraujoch for Jungfrau – temperatures outside will be below freezing, December average is around -12°C.
For Titisee in Germany expect also temperature around freezing – average maxima around 5°C
Paris weather for December is usually above freezing, but don’t expect temperatures above 10°C
There are lots of websites with climate information, for instance
www.weatherbase.com/weather/country.php3… or http://www.worldweatheronline.com/ …
So get rain and wind protection for near freezing temperatures for most of your trip to -10°C for the higher altitude Alps area.