Sönke is a lawyer admitted to the bar in Germany and Spain and has been based in Madrid since 2004. Initially, Sönke worked for 12 years as a litigation lawyer before Spanish courts and arbitration tribunals, representing German-speaking companies. From 2009 onwards, as head of a litigation department, his contentious and advisory work focused primarily on investments in renewable energy in Spain.

In 2015, he founded his own law firm specialising in energy law in close collaboration with Dauss (Barcelona). This successful partnership led to the creation of Schlaich Dauss SLP, focused on investments and contract drafting, as well as advising public administrations in the energy sector.