With the mesh object selected,
obj = mc.ls(sl=True)[0]
vertCount = mc.polyEvaluate(obj, v=True)
vertList = ['{0}.vtx[{1}]'.format(obj,vert) for vert in range(vertCount) if len(mc.polyInfo('{0}.vtx[{1}]'.format(obj,vert), ve=1)[0].split(':')[1].split()) == 2]
mc.select(vertList)
# Result: u'VERTEX 302: 506 489 484 485 \n' #
UPDATE: A vertex sharing two edges is called 'winged'. Here's another way to select winged vertices using PyMEL (as pm)...
obj = pm.ls(sl=True)[0]
vertList = [obj.verts[v] for v in range(len(obj.verts)) if len(obj.verts[v].connectedEdges()) == 2]
pm.select(vertList)

