I have a floor joist where the knot in the middle of the span is somewhat coming out. Attached is a picture. Should I be worried and how do I fix it?
It always happens and was a total miss by the framing crew. But, unless you're springy upstairs it's not really a problem. The adjacent joists will assist just fine for normal empty area loads above.
Although, if you have the ability to address it, then even a 2x4 glued and liberally screwed to one side can remedy any perceived weakness. Preferably, the 2x4 should run a minimum of 3-feet out on either side of the knot, hole, notch or weak spot.
I would not get too excited.
Reason 1: that knot has been allowed for in the grading of the lumber. If #2 framing will do the job as designed, you don't need to repair every little defect in an attempt to make structural select out of #2.
Reason 2: floor joists are part of a system, where loads are shared by many floor joists working together.
If you can't bear to do that, remove or rip open the drywall for access and sister a hunk of lumber beside that area, extending several feet on either side of it. You'll also have to relocate the cables that are presently stapled to it to do that.
Using a steel reinforcing strap/plate is also an option. That might fit below the cables.
That knot was always a weak spot, and the drywall screw that separated it has not made it significantly weaker.
You could add cross blocking to the two neighbouring joists, but really this is much ado about nothing.
Cosmetic damage to a piece that will soon be hidden behind drywall, just let it be.
Overall, it's structurally sound due to redundancies built into neighboring joists.
The frustration will arise if you go to step on that spot from above and start hearing a squeak. That is a prime location for nail pops in subfloor or hardwood.
If you have a drywall seam on that joist or close to it then it has a chance of cracking after it's mudded. Is this parallel seem running in an open air space?