Should "uncomment" include a hyphen like this: "un-comment", or either one correct?
The use of un as a prefix is part of normal grammar, and it is typically used without a hyphen when it precedes a word starting with a consonant. In looking at the Merriam-Webster definition of un, none of the example sentences use it in a hyphenated form.
Where it is used with a hyphen, it's when the word that follows it starts with a vowel, such as un-American, un-English, and un-European, and where not using a hyphen could lead to confusion in interpretation.
Google Books NGram Viewer also shows that uncomment is far more common that un-comment. (And since people don't speak punctuation, the existence or nonexistence of the hyphen in speech is both irrelevant and nonsensical.)