A man of understanding.
v.5 Deep water. The purpose in a man’s heart (perhaps advice or motive) is hard to discern, like deep water (profound thought), but a man of understanding will draw it out (like water out of a deep well). See 18:4.
v.6 A faithful man. Many men proclaim their own steadfast love (loyalty), but who is able to find a faithful (reliable) man? (Eccl 7:27-29) The true friend stands by you even through difficult times (17:17). The proverb indicates that it is rare (or impossible?) to find someone on whom you can really depend.
v.7 Integrity. Blessed are the children (descendants) of the righteous person (who believes in the Lord) who walks in integrity (lives out his life according to his faith), see e.g. Ps 112:1-2.
v.8 Judgment. The king who sits in judgment carefully distinguishes between the bad and the good. The wicked will be separated from the righteous and duly punished (v.26).
v.9 Pure heart. This is a rhetorical question (the answer is none). Wise people see their weaknesses but pride prevents the unwise from seeing their faults. No one is without sin (Rom 3:23).

Read Proverbs 20:5-9