QGIS for Mac (KyngChaos version) is an application bundle ( directory) and the content of QGIS.app is:

The path of the modules is
/Applications/QGIS.app/Contents/Resources/python
The path of the qgis library is
/Application/QGIS.app/Contents/Resources/python/qgis
And of the processing module, for example:
/Application/QGIS.app//Contents/Resources/python/plugins/processing
If you want to call qgis from outside (in the console, for example), you have two solutions:
1) Define the variables/paths outside Python (Bash)
export PYTHONPATH=/Applications/Qgis.app/Contents/Resources/python
# you can add other modules
export PYTHONPATH=/Applications/Qgis.app/Contents/Resources/python/plugins:$PYTHONPATH
(export PYTHONPAH=/Users/you/.qgis2/python/plugins:$PYTHONPATH if you want)
and
python
.....
from qgis.core import *
QgsApplication.setPrefixPath("/Applications/QGIS.app/Contents/MacOS", True)
QgsApplication.initQgis()
# initialize the app
app = QgsApplication([],True)
layer = QgsVectorLayer('/Users/Shared/test.shp', 'test', 'ogr')
layer.isValid()
True
print QgsApplication.showSettings()
Application state:
QGIS_PREFIX_PATH env var:
Prefix: /Application/QGIS.app/Contents/MacOS
Plugin Path: /Application/QGIS.app/Contents/MacOS/../PlugIns/qgis
Package Data Path: /Application/QGIS.app/MacOS/../Resources
Active Theme Name:
Active Theme Path: :/images/themes//
Default Theme Path: :/images/themes/default/
SVG Search Paths: /Application/QGIS.app/Contents/MacOS/../Resources/svg/
User DB Path: /Application/QGIS.app/Contents/MacOS/../Resources/resources/qgis.db
# import a module
import processing
print processing.__file__
/Application/QGIS.app/Contents/Resources/python/plugins/processing/__init__.pyc
2) Define the paths in Python
python
....
import os
import sys
sys.path.append('/Applications/QGis.app/Contents/Resources/python/')
sys.path.append('/Applications/QGis.app/Contents/Resources/python/plugins')
....