Meaning of “take a knee”

Ice Cube's intro in his newest album starts with

Yeah, you know me. Super OG.
Always down to take a knee.

What does this last sentence mean? He won‘t literally take someone’s knee I guess..

Solution 1:

Semantically

The meaning of "take a knee" is very similar to "take a seat".

phrase
formal

If you take a seat, you sit down.

• 'Take a seat,' he said in a bored tone.
• Rachel smiled at him as they took their seats on opposite sides of the table.

The difference between "take a seat" and "take a knee" is that with the latter, you kneel instead of sit.

Contextually

The lyrics are not just focusing on the semantical meaning. They are in reference to a recent form of activism centered around NFL player Colin Kaepernick, who chose to kneel for the American anthem (when it is customary and expected to stand up) as a way of peacefully protesting because America is (quote Kaepernick) "a country that oppresses black people and people of color".

This sparked a wave of people taking a knee in support of both Kaepernick (who received backlash for his activism) and Kaepernick's cause.

Contextually, "taking a knee" can thus mean "show your support". Your quoted lyrics can be translated as

Yeah, you know me. Super OG.
Always willing to show my support for causes I believe in even if it causes me to receive backlash.

But this translation doesn't quite flow enough to be used for the actual lyrics.