Which parts of this U.FL laptop wifi antenna need to be exposed?
Ideally, to get the best performance from such an antenna, there should be no metal whatsoever in the vicinity of the antenna. If you keep any metal further away than, say 10 cm (a guess I sucked out of my thumb!), the antenna's radiation pattern should not be that much affected. This type of antenna that you show radiates in all directions more or less equally.
Metal reflects the signal that the antenna is radiating. If there is metal too close it blocks the signal in that direction but also the signal can reflect back into the antenna preventing it from &quot;getting out&quot;!
So when you're using a metal case/housing and are not using external antennas then you will have to accept a compromised antenna performance. This type of antenna isn't designed to be used near a metal surface.
If you have no alternative then my choice would be to make a hole in the metal case through which the cable and connector can fit. Then keep the PCB outside the case, the cable can be inside, that is no issue.