We found one dictionary that defines the word have a head on one's shoulders:

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1. have a head on one's shoulders: Wiktionary

Definitions from Wiktionary (have a head on one's shoulders) ▸ verb:  To have good sense or judgement. ▸ Words similar to have a head on one's shoulders ▸ Usage examples for have a head on one's shoulders ▸ Idioms related to have a head on one's shoulders ▸ Wikipedia articles (New!) ▸ Words that often appear near have a head on one's shoulders ▸ Rhymes of have a head on one's shoulders ▸ Invented words related to have a head on one's shoulders