What a Muslim cannot be ignorant of

What a Muslim cannot be ignorant of

“…what is necessary for everyone to know is the obligations upon each individual, 
from the shahadatayn and testifying in their hearts 
   that Allah is One and He has no partners, 
   and there is none like Allah — He does not beget nor is He begotten, 
   [He is] the Creator of everything, 
   and to Him is the return of everything, 
the Giver of life and death, 
the Ever-Living that does not die. 

What Ahlus-Sunnah are upon is that He always had His Attributes and He still has His Attributes and Names, He has no beginning and He has no end, and He is above His throne.

Testifying that Muhammad (peace and blessings of Allah be upon him) is His slave, messenger, and final prophet is the truth. 
That the resurrection after death to reward and punish people.
That eternal life in the hereafter for the successful is in Jannah, and for the people of disbelief and ingratitude is in Jahannam. 
That the Quran is the word of Allah and what is in it is truth from Allah, and that we must believe in all of it and understand it holistically. 

That the five prayers are an obligation, and that he needs to know what, without it, the prayer is not valid, from matters of purification and the rest of the ruling.
That fasting Ramadan is an obligation, and that he needs to know what, without it, the fasting is not valid. 
If he was a person who possesses money, then he must know what the zakat is issued on, when it is due, and how much it would be. 
If he possesses money and has the ability to perform hajj, then it is obligatory for him to know that he must perform hajj once in his life if he is able to...
...To matters that he must know it in generality is not excused for not knowing it, such as 
   [the prohibition of] zinah and riba;
   and such as the prohibition on khamr, pigs, eating the flesh of meat that died without slaughter and that which is impure; 
   bribery, false testimony, consuming peoples money unjustly;
   that oppression is prohibited as a whole;
   that marrying the mothers, sisters, and those who have been mentioned alongside them is prohibited; 
   and that the unjust killing of a believing soul is prohibited;
   and that is which like all of this that the Book has spoken about and that the Ummah has a consensus upon.”
— Qāḍī ibn ʿAbd al-Barr (raḥimahullāh)

ما لا يسع المسلم جهله
by صلاح الصاوي
~~~

“…Indeed, that which is most obligatory upon a Muslim is
   knowledge of 
     [the aspects of] the creed of the Deen [of Islaam] 
     & what Allaah has obligated upon His Servants 
   (including the understanding of His Tawheed & of His Attributes, and believing in His Messengers, with evidences & with certainty)
   arriving at [all of] that and seeking evidences for them with clear proofs.

And among the mightiest of statements and clearest of proofs and understandings is:

[1] The Book of Allaah, the Manifest Truth,
[2] Then the saying of the Messenger of Allaah ﷺ,
[3] And of his Companions, the chosen, pious ones, 
[4] Then that which the Salaf us-Saalih were unanimously agreed upon,
[5] The holding fast to all of that and remaining firm upon it till the Day of Judgement, 
[6] Then turning away from the innovations and from listening to them – from amongst those things the astray people have invented.”
— Imām al-Lālikāī (raḥimahullāh)