In 2 Peter 1:1-8, there there are two words translated into English as "knowledge".
The two words generally translated as 'knowledge' are 'gnosis' and 'epignosis'. Whereas 'gnosis' conveys the idea of just 'knowing', 'epignosis' is a knowledge that involves a 'full discernment', which is 'to become fully acquainted with' or to have a full understanding of something.
Here is the text:
"Simon Peter, a servant and an apostle of Jesus Christ, to them that have obtained like precious faith with us through the righteousness of God and our Saviour Jesus Christ: Grace and peace be multiplied unto you through the knowledge (epignosis/full discernment) of God, and of Jesus our Lord, According as his divine power has given unto us all things that pertain unto life and godliness, through the knowledge (epignosis/full discernment) of him that has called us to glory and virtue:
"Whereby are given unto us exceeding great and precious promises: that by these you might be partakers of the divine nature, having escaped the corruption that is in the world through lust.
"And beside this, giving all diligence, add to your faith virtue; and to virtue knowledge;(gnosis/knowing)
And to knowledge (gnosis/knowing) temperance; and to temperance patience; and to patience godliness; And to godliness brotherly kindness; and to brotherly kindness charity.
"For if these things be in you, and abound, they make you that ye shall neither be barren nor unfruitful in the knowledge (epignosis/full discernment) of our Lord Jesus Christ.(II Peter 1:1-8)
It seems that Peter is saying that we are called as disciples to do more than just know the gospel, or to know that it is real and good and accept it and follow "the commandments or the words of the prophets", but rather the message here is that it is essential that we continue, all our lives, to grow in faith, virtue, further general knowledge, temperance, patience, godliness, brotherly kindness and charity/love in order to truly comprehend Christ and to comprehend and live His gospel.
(You can read more about that in this link:
https://biblefocus.net/living-word/knowledge/index.html )
Being able to say "I know the gospel is true", or "I know that [insert anything you think is true] is true', is not what we are called to aspire to be able to do. That is not the "requirement for an acceptable level of sufficient belief or knowledge" that we must aspire to, or worry about if we cannot honestly declare it.
What is required? That we welcome the Lord into our life in a way that opens us to learning, from Him (how to become more like Him in faith, virtue, knowledge, temperance, patience, godliness, brotherly kindness, and charity towards others), and that as we engage in that communion with Him and in His work we, by his grace, increase our capacity to see as He sees, know as He knows, and show forth grace (a ready willingness to help) towards others as He does.
That's what we are called to when God speaks about "knowledge". It is not an "I have arrived, I know such and such" kind of thing. It is a lifelong communion with God and His grace in our discipleship.