What vowel sound is in the word look?

The word look is spelt in IPA pronunciation as /lʊk/ - the vowel sound ʊ refers to a near-close near-back vowel.

This is called a "short OO" vowel sound because it does not have the same force as a long OO (long U) although it is spelled the same. Examples of this (oah) sound are book, good, foot, and put.