It’s possible to be added to someone’s insurance policy as a named driver. Often, the spouse / partner can be added at no cost. Younger drivers such as children will increase your insurance premium.
Many policies include the possibility to add a short term driver at no or very small cost. You can contact your insurance and just get the name added. The exact length and amount of additional driver differs by insurer.
Some policies do not offer the option to add another driver. You can then get a temporary additional insurance (Zusatzpolice Kfz-Versicherung) through another car insurer. Please contact your insurer directly, Joonko does not offer any temporary coverage.