Its complicated. You can approximate it using the 2-star-center-of-mass, but thats skipping over important stuff.
See, the stars are orbiting one another. At any time one may be closer/further away than the other from the planet. That makes the COG appear to 'wobble'.
IF the planet is in something like a 'lagrange point' where it always sees both stars in the same relative position, then the COG approximation is true. Otherwise the planet will behave in a more complicated manner, and in fact may not have a stable orbit at all.
See, the stars are orbiting one another. At any time one may be closer/further away than the other from the planet. That makes the COG appear to 'wobble'.
IF the planet is in something like a 'lagrange point' where it always sees both stars in the same relative position, then the COG approximation is true. Otherwise the planet will behave in a more complicated manner, and in fact may not have a stable orbit at all.