Hello, please try to press space to deselect everything. This will allow to see all the keys in the dopesheet for the active skeleton.
If no key pops up in the first row of the dopesheet on frame 40, then check if you have any dopesheet filter on (that you need to deactivate), or if you hid bones in the hierarchy (you will need to activate them as hiding them in the tree also hides them in the dopesheet).
Please let me know if you still encounter problems after trying these solutions!