The Observe Bone node can be used to give debug transform information about a specified bone.
Below, a bone by the name of b_MF_Hand_L is being observed and debug information is being displayed.
Bone to Observe
Name of the bone to observe.
Reference frame to display the bone transform in.
Relative to Ref Pose
Whether or not to show the difference from the reference pose.
The incoming pose.
Observe Bone nodes are also affected by the LOD Threshold system introduced in 4.11. You can find the setting for this in the Details Panel for the Observe Bone node.