Karl doesn't work in a surgery..
If I recall correctly:
Karl used to run the local medical practice in Erinsborough. Though a former GP, Karl seemed to be trained in every field of medicine possible, as he has been directly involved with every aspect of any medical problem to happen in Erinsborough since his arrival in 1994, including mental health problems and births.
Having admitted being tempted to stray on many occasions, his first actual act of infidelity happened when he kissed Sarah Beaumont (his receptionist at the time). Susan (Jackie Woodburne) found out some time after the incident through their son, Billy. She slapped him and threw him out. She eventually forgave him, but they separated after Susan developed retrograde amnesia and forgot everything that happened after 1972, including her marriage to Karl and the birth of their children. They eventually reconciled, but separated again some time after and divorced after nearly 30 years of marriage. The divorce was amicable with Susan keeping the family home. Karl found love in the considerably younger Isabelle Hoyland (Natalie Bassingthwaighte) who seduced Karl. She later got pregnant by Gus Cleary (Ben Barrack), and led Karl to believe he was the father of her baby. She had been informed that any other pregnancy was unlikely. Izzy later miscarried. When Susan discovered the baby was not Karl's, with help from her nephew Darcy Tyler (Mark Raffety), she gave Isabelle an ultimatum - she had to tell Karl the truth within 24 hours or she would tell him herself. Eventually the relationship collapsed. Karl nearly died after having a heart attack on a lonely road. Convinced any phone call he made would be his last, he called his ex-wife Susan, making him realise that he had made a mistake divorcing Susan although another reconciliation seems unlikely. Karl began a relationship with Jenny, a local Councillor, who is not popular amongst other Ramsay Street residents. At one point she even pretends that she is engaged to Karl. This relationship ends when Karl realises he is still in love with his ex wife Susan. Karl was a mentor for Zeke Kinski (Matthew Werkmeister), helping him with school work and football, since Zeke's father (and also Susan's second husband) Alex Kinski (Andrew Clarke) died. Susan and Karl have since got back together, but had to stop seeing each other because Rachel (Caitlin Stasey) and Zeke, Susan's stepchildren, thought that she was betraying their late father Alex.
Susan and Karl's relationship got back on track soon though. Karl has now moved back into the Kinski household, reuniting Susan and Karl in their marital home. After the paternity mix-up with infant Kerry Mangel, Sky Mangel (Stephanie McIntosh) considered sueing him but abandoned the idea though Karl decided to quit his career as a doctor and has now taken up home farming, selling home grown eggs.
The long-running series in-joke that Karl's middle name was "Marx" due to his adoptive father's supposed Communist leanings (hence his first name being "Karl", making his name "Karl Marx Kennedy") was finally addressed with the appearance of Karl's biological father, who confirmed that his middle name was actually "Raymond". Although, in the March 19, 2007 episode, Karl made a reference to Karl Marx while spelling out his name to footballer Pete Gartside (Daniel Schutzmann), during a trip to England with Susan.
While in England, Karl accidentally booked a shared room in the Ritz Hostel, not the Ritz Hotel. While Susan was enraged with Karl with this at first, she later forgave him. Later on in the trip, Karl proposed to Susan, who accepted. Both were extremely surprised to discover that the heavily-pregnant Izzy was also in England, having an affair with the footballer Pete Gartside. When Karl threw a surprise wedding a few days before they left for Ramsay Street, Izzy decided she was going to tell Karl that he was the father of her child. Both Pete and Izzy snuck on board the boat Karl and Susan were getting married on, and she fell into labour after they were officially married. Karl delivered Holly Hoyland, but did not know she was his own child. Susan overheard Izzy and Pete talking in the ambulance that Karl was the father, but she kept this from him until they arrived back in Ramsay Street. Karl then returned to London to see his new daughter.
When he came back, he found out that Tom Scully had returned and was the new principal of Erinsborough High School. Karl was upset that Susan never told him that Tom was back in Ramsey Street. Karl is currently working for Davo Mather.