knob / nob are similar-sounding terms with different meanings (referred to as homophones). To better understand the differences, see below for definitions, pronunciation guides, and example sentences using each term. 👇
knob: (noun) a circular rounded projection or protuberance. (noun) a round handle. (noun) an ornament in the shape of a ball on the hilt of a sword or dagger.
nob: NA
knob: n·AA·b
nob: NA
(Examples are Wikipedia snippets under the CC ShareAlike 3.0 license. Definitions drawn from WordNet.)