Jahnke is of Samoan-German-Irish-Maori descent and works as a contemporary sculptor. He received a Bachelor of Fine Arts in Industrial Design and a Master of Fine Arts in Graphic Design from Elam, and continued to study further in California. He then returned to New Zealand and taught in Hastings, Rotorua and Palmerston North. His works are based on Maori-Pākehā relations, and involve a range of found objects such as steel and lead.