What song has Do do doo Towards the ending being sung over a small guitar riff rock almost ballad esque?

The song you're thinking of is "Sweet Child o' Mine" by Guns N' Roses. It was released in 1987 and is one of the band's most popular songs. The song features a memorable guitar riff and a vocal performance by Axl Rose that includes the "do do doo" part you mentioned. The song is a rock ballad and has been a staple of classic rock radio for decades.