This sentence follows the third conditional structure: If + past perfect, then would have + past participle. Since the first part is "had known", the result must be "would have gone".

১. "I would go" is part of the second conditional, used for hypothetical present situations.
২. "I had gone" cannot be used as the result clause in a conditional sentence.
৩. The third conditional is used to express regret or things that didn't happen in the past.

অতিরিক্ত তথ্য: If clauses are essential for expressing various levels of possibility in English grammar.