Question

we went to santa fe , which is the second oldest city in the united states which is the linking verb

Answer 1

There are only two verbs in the sentence 'went' and 'is' so it must be 'is'. However the word 'which' acts as a conjunction which thus links the two things together. Without the 'We went' bit it would be 'Santa Fe is the second oldest city in the US.'

Answer 2

i would say oldest is the linking verb