Supposedly is pronounced sə-POH-zəd-lee (IPA /səˈpoʊzɪdli/). There's no 'b'; say 'suh-POH-zed-lee' with a 'd' before 'lee'.
IPA: /səˈpoʊzɪdli/
Syllables: sə · POH · zəd · lee
Common ESL mistake: Learners insert a 'v' saying 'sup-POSE-uh-blee' or 'sup-POSE-ah-blee'.
Tip: There's no 'b'; say 'suh-POH-zed-lee' with a 'd' before 'lee'.