As‑salāmu ʿalaykum wa raḥmatullāhi wa barakātuh. What falls under obligatory knowledge? For example: do the rights of travellers and friends also fall under it? Jazākallāhu khayran.

Ustadh AbdulAziz al-Haqqan

Necessary knowledge in regards to Tawheed, Aqeedah, and the acts of worship that you need and you do: you have to learn them correctly in order to do them correctly.