That is pronounced THAT (IPA /ðæt/). Start with the voiced 'th' as in 'this', then a clear 'at'.
IPA: /ðæt/
Syllables: THAT
In 62 attempts by 26 learners scored in the SayWhat app, the sound most often scored red in this word was /ð/ (16% of attempts).
Common ESL mistake: Learners say 'dat' or 'zat' replacing /ð/ with /d/ or /z/.
Tip: Start with the voiced 'th' as in 'this', then a clear 'at'.