There's two problems:
1- To sort by second value of key-tuple, you forgot the .items() invocation
>>> print sorted(d.items(), key=lambda item:item[0][1])
[(('08', '10010'), 6), (('23', '10017'), 6), (('21', '10027'), 6), (('06444', '10028'), 6)]
2- If you need a dict where keys are sorted by that criteria, you need an OrderedDict object, because in a default dict keys' order is not guaranteed
>>> print dict( sorted(d.items(), key=lambda item:item[0][1]))
{('23', '10017'): 6, ('21', '10027'): 6, ('08', '10010'): 6, ('06444', '10028'): 6}
>>> from collections import OrderedDict
>>> print OrderedDict( sorted(d.items(), key=lambda item:item[0][1]))
OrderedDict([(('08', '10010'), 6), (('23', '10017'), 6), (('21', '10027'), 6), (('06444', '10028'), 6)])