He completed his neurosurgical training in Australia, and subsequently undertook subspecialty training in Stereotactic and Functional Neurosurgery (including stereotactic radiosurgery) in Calgary, Canada and UCLA, Los Angeles. Dr Jonker has a particular interest in conditions treated with stereotactic and functional neurosurgery – and treats these with both conventional neurosurgery and stereotactic radiosurgery. His main interests are brain and pituitary tumours including awake surgery and brain mapping, trigeminal neuralgia, movement disorder surgery and endoscopic surgery for hydrocephalus.