Both 2) and 3) are OK. The underlined portion functions as an adjective, specifically an adjective phrase, headed by a relative pronoun. The pronoun and the verb can be omitted (...). In fact, they are often omitted.
2a) Give me something (that is) hot.
2b) Give me something hot.
3a) Let's go somewhere (where it is) quiet.
3b) Let's go somewhere quiet.
In 3) the noun 'somewhere' is synonymous with someplace. (US English)
a) Let's go someplace where it's quiet.
b) Let's go someplace quiet.
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