When the wind is from the west, the runways at CDG operate in the east-to-west direction. This is the most common direction.
On arrival there will be no chance to see the Eiffel Tower. Arriving flights are generally routed directly towards the runway, and as you're arriving from the east the flight path will not go anywhere near the tower.
When departing towards the west, you might be able to see the Eiffel Tower in the distance to the left of the aircraft, a few minutes after takeoff. Your closest approach to it will be about 16 km, at a time when you will be 1 to 1.5 km from the ground. That's high enough that you shouldn't look too close to the horizon, but far enough away that you can easily miss it unless you have prepared in advance, memorizing an (upside-down) map of Paris so you know where to look.
And many departing flights towards the northwest will start banking towards the right before they reach that point, in which case you have no chance there either.
When the wind is from the east, the runways operate west-to-east.
In this situation there's a pretty good chance (say about 50%) that your arriving flight will pass to the south of the airport before making an U-turn to align with the runway. This path will take it quite close to central Paris, so you should be able to get a pretty nice view of the Eiffel Tower and other landmarks in the center if you sit on the left side of the plane.
On the other hand, there's also a chance that the flight path will take you north of the airport instead, in which case you're out of luck again.
When departing towards the east, the chance of getting to see the tower is extremely slight. All the Flightradar tracks in this situation I can find turn away from Paris shortly after takeoff.
Beware that sitting on the left would also probably mean that you will have the sun shining through your window for much of the flight (depending on the time of day).