You could do something like the code below.
If you are trying to understand the modules, you can also benefit from peeking through the source code on dynamo and dynamo revit repos (https://github.com/DynamoDS/Dynamo/tree/master/src)
is_callable = []
docstrings = []
for attr_name in dir(DocumentManager):
attr = getattr(DocumentManager, attr_name)
if hasattr(attr, "__call__"): # True is callable
is_callable.append(attr)
docstrings.append(attr.__doc__)
# output and inspect is_callable and docstrings
(did not run code, might have errors or typos! :))
