The minimum obligatory knowledge is the basic faith (Tawheed, Adl, Nubowwah, Imamat, Qiyamah) and day to day matters which you need it like Wudhu, Ghusl, Tayammum, Salah rules and what to do when you doubt the number of Rak'ats, fasting, Khums, Zakat, Am Bil Ma'roof and Nahi Anil Munkar, Halal food rules, family rules, Hijab rules, etc.
Wassalam.