You can set fiducials or use a curve node. you can place the curve points manually or use SlicerVMTK extension’s Extract centerline module to do it automatically from airway segmentation: you can extract the entire bronchial tree automatically then mark two points between them, and use the resulting curve as input in endoscopy module.
Airway segmentation:
Finding path between two points in the bronchial tree:
After this, you can resample the curve to a new curve in Markups module and use the resulting curve in Endoscopy module. Or you can straighten the selected branch using Curved Planar Reformat module (in Sandbox extension) to make it easier to traverse and make measurements.