The lyric you’re thinking of is from “Jordan” by Emmylou Harris, featuring Johnny Cash. The refrain goes, “Oh what, what you gonna do? / Oh what, what you gonna say? / Oh how, how you gonna feel? / When you come to the end of the way.”

Quick Scoop

This is a gospel song, not a fast country duet in the usual sense, and it appears on Emmylou Harris’s Roses in the Snow album, released in 1980. It’s one of those songs that sticks because the question in the chorus sounds plainspoken but heavy, which fits both artists’ voices really well.

Song match

Your line sounds like a slightly misremembered version of the chorus. The key phrase is “when you come to the end of the way,” and the repeated response is “what you gonna do / what you gonna say / how you gonna feel.”

Context

Johnny Cash’s presence makes the track especially memorable, since the pairing of his deep vocal style with Emmylou Harris’s harmony gives the song a solemn, reflective feel. The song is about facing life’s end and spiritual accountability, so the repeated questions are meant to land like a warning and a call to reflection.

TL;DR: You’re almost certainly asking about “Jordan” by Emmylou Harris featuring Johnny Cash.