Does Jupiter lose some atmosphere at all? I've hear of something like this: "All planets lose their atmospheres eventually and they become a barren rock if given enough time."

There are three types of atmospheric loss ways:


Jeans Escape: Temperature and escape velocity factors determine the gasses and the amount that's lost. Jupiter cannot lose atmosphere via Jeans escape because Jupiter has too high escape velocity and too high of a temperature.
Charge exchange: Solar radiation creates electrons and positively charged ions in upper atmospheres by tearing electrons off atoms or molecules. Subsequently, charge attraction and repulsion in collisions accelerates ions. Jupiter most likely cannot lose its atmosphere via charge exchange because its magnetic field is strong and extensive while no(little?) material escapes via polar wind.
Vertical atmospheric escape/impact erosion: Energetic objects that strike a planet erodes its atmosphere by creating a plume of heated gas. Jupiter does not lose its atmosphere via impact erosion because it has very high gravity and escape velocity. This pulls particles ejected by impact back into its atmosphere.


Since Jupiter doesn't lose atmosphere in the three types of atmospheric loss, how does it lose its atmosphere?
The phrase you hear is correct! Atmosphere will always be lost, no matter if it is a star or planet. Stars lose their mass via solar wind. Planets lose theirs via the three types of atmospheric loss you mentioned. Frozen planets lost their atmosphere thru sublimation and other things such as ionization. So, yes Jupiter does indeed lose its atmosphere. 

You compared the three types of atmospheric loss and how they relate to Jupiter. This is where you assumptions turn out to be wrong. The thermal loss aka Jean's escape affects Jupiter even though it may seem to be not affected in the chart. Periodical or random heat generated by things could excite particles enough to overcome the escape velocity.

The solar wind, even with Jupiter's extensive magnetic field, will reach the atmosphere and neutralize atoms, which in turn will then not be effected by the magnetic field and drift off.

Jupiter is also prone to bombardment from asteroids and comets and other solar system junk. These can range from large sizes such as Comet Shoemaker-Levy 9, to minute small pieces that are barely larger than a pea. These impacts, though they add a considerable amount of stuff into Jupiter, eject mass into space, even with such strong gravitational pull via vertical atmospheric escape, creating a hot plume of material that rises and escapes from a planet. This effect nullifies most material Jupiter gains from the collisions.

Then, will all things added together, we see that Jupiter is gaining mass only via collection of objects, which in turn removes mass from Jupiter via vertical atmospheric escape. This means only a small portion of all mass collected by Jupiter this way is a gain. Now, subtract off thermal and charge exchange escape from the gain, and you will see that Jupiter is not really gaining any material, but rather losing it. Over time, if enough is given, Jupiter will only be a barren core.