Have all the workers of iniquity no knowledge? who eat up my people as they eat bread, and call not upon the Lord.
Psalm 14:4 KJVS
Which type of knowledge is being addressed here, in Psalm 14:4?
The question is speaking of self destruction. We need that clarified first, since we all have knowledge; some more than others. One may have knowledge of medicine but have no knowledge of gardening. In such a scenario, the wise doctor is a fool in gardening. Now, as to the knowledge being referred to in the question asked by the psalmist:
Proverbs 1:7 The fear of the LORD is the beginning of knowledge: but fools despise wisdom and instruction.
Scripturally, knowledge begins with and centers on knowing God. Therefore, ‘the wise’ is the person who knows God, while the fool is the person who does not know him.
Consider upon this: someone can be wise in this world but seen as foolish to God, as well, someone can be a fool in this world but wise before God!
Now to the question, do workers of iniquity have no knowledge?
Consider: We all were workers of iniquity until we came to know the LORD.
Recommended reading The Day of the Lord
Here we see how this question (in Psalm 14:4) testifies / concerns Jesus, because it is through him that we are able to get knowledge (know God) and through that knowledge escape the pollution of this world – 2 Peter 2:20
The knowledge of God brings us out of darkness: For God, who commanded the light to shine out of darkness, hath shined in our hearts, to give the light of the knowledge of the glory of God in the face of Jesus Christ – 2 Corinthians 4:6
The idea is, knowing God changes us; this is why God said the people didn’t know him when they continued to live faithless (sinful) lives (Psalm 95:10) after he brought them out of Egypt.
Forty years long was I grieved with this generation, and said, It is a people that do err in their heart, and they have not known my ways:
Psalm 95:10 KJVS
It is also connected to why he said one cannot see him and live. Because it’s impossible for us to get to know|see God and continuing our fleshly lives as we knew it.
Therefore, a “worker of iniquity” doesn’t not have knowledge i.e. they have not seen… they do not know God. As such only when they come to Jesus, will they get knowledge of Him.
If ye had known me, ye should have known my Father also: and from henceforth ye know him, and have seen him.
John 14:7