Even though the Be-er 'Eseq permitted reciting a Berakha (blessing) over Setham Yenam (non Kosher wines), many Posqim disagreed with him and said that one may not recite any blessing on it, neither before nor after.
If a person ate forbidden food in a situation of danger, such as if he is ill, Heaven forbid, the Shulhan 'Arukh says that he should recite a blessing over it. If possible, he should include something permitted with it. If that is not possible, it says in the Kaf Hahayyim, that he should say the blessing in his mind.
All this assumes that he actually enjoyed what he ate, but if not, he should not recite any blessing at all. If a person was threatened and forced to eat non Kosher food, even though it would be dangerous if he refused, he should not recite any blessing.
(See Shulhan 'Arukh 196:2. Mishnah Berurah, ibid., 5, 6. Kaf Hahayyim, ibid., Oth 8)
Stam Yeinam, Brocho, Bracha, Berakha