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TI-BASIC, 13 bytes
Tested on my TI-84+ calculator
29.11-dayOfWk(Ans,9,1
Thankgiving is November 29, minus the day of the week of September 1st, where 1 is Sunday and 7 is Saturday. This outputs in the format DD.MM.
Test cases: 2015 gives 26.11, 1917 gives 22.11 have been verified.