Is the word know ever plural?

Answer 1

The verb know is used with first and second person singular:

I know, you know.

It is also used with first, second and third person plural:

we know, you know and they know.

For third person singular, you must use knows:

he knows

she knows

it knows

Answer 2

No, the word "know" is never used in its plural form. It remains the same whether used in singular or plural contexts.