riddle - I may also be found in your body

My infix won't tell you a thing,
But you can find me from the rest:
My suffix sounds exactly like me,
And my prefix is already half known.

In wood or wire, what am I?

Answer

You are a:

Knot

My infix won't tell you a thing,

"no"

My suffix sounds exactly like me,

"not" is pronounced just like "knot"

And my prefix is already half known.

"kno" is half of "known"

In wood or wire, what am I?

Knots in wood, and knots in wire are both very common.

I may also be found in your body.

You can also have a knot in a muscle.