In this example, I create a group. Inside that group there is a simple backdrop node. To that node is added a Color_Knob. Now, adding a knob to a node is rather simple. But when it’s time to add this knob to the group it lives in, (also known as “pick knob” in Manager User Knob) is might seem not so intuitive.
Here’s an example.
group = nuke.createNode('Group')
group.begin() # Enter the group
bd = nuke.createNode('BackdropNode')
colorPicker = nuke.Color_Knob('position','Position') # Create a color picker
bd.addKnob(colorPicker) # Add the color picker
link = nuke.Link_Knob( 'linkedSizeKnob' )
link.makeLink('BackdropNode1','position') # Make a link of the color picker
group.end() # Exit group
group.addKnob(link) # Add link knob to group node (similar to pick knob in Manage User Knob)