Fard ul `Ayn is that which is obligatory upon every Muslim. This will include actions, as well as knowledge of them. For example, Salah, Fasting, Zakah, and Hajj are all Fard (obligatory) upon every Muslim.
These actions are Fard, knowing the detailed obligations of them is also a Fard. This will extend to all that a Muslim interacts with on a daily basis, for example, if a Muslim owns a business, it is a Fard for them to understand the rules and guidelines pertaining to business.
The Shaykh advises us to seek knowledge of that which is Fard for us. It is extremely important to be well versed with the Fiqh of Salah, Fasting, Zakah etc as knowledge of the action is what determines validity to it.
Imam Ghazali 
, the great scholar, once said,
“Knowledge without action is madness, and action without knowledge is void.”
Based on this alone, we learn that our actions count for nothing if we don’t understand what it is we are doing. For example, Aqeedah is a Fard to learn. We see that the more we come to know of Allah ﷻ, The Exalted, the more our hearts become attached to Him. This runs true for any action that is Fard for us, and should be one of the reasons we strive in gaining this knowledge.
This is only a very brief introduction to what is Fard ul `Ayn. Every seeker is encouraged to go out and fulfil this command.