I just knitted a dishcloth and there was a knot in the wool. I'm afraid it might come apart when I use it. Is there anything I can do so it won't come apart/
I think it is too late to ask. If it were I, I would rip out to that point, cut out the knot, and start that row over, being sure to leave a tail long enough to weave into the fabric. Or use a Russian Join.
Was it wool or another yarn? If you don't want to frog it and start over, you can use a needle and matching thread and run a few stitches through the knot or try putting a dab of liquid thread glue like Fray Check (Joann's sells it) on it.