Can an electrolytic capacitor discharge through its top?
In all cases that I'm familiar with, the case of an Aluminum electrolytic capacitor is connected to the (-) lead on the part.  In cases like axial-leaded devices this is often obvious as you can see the lead connected to the case at the end.
With radial-leaded devices this may be less obvious but it's almost certainly connected.
That's one reason for the shrink-wrapped plastic covering that covers these devices.
For low-voltage circuits you would be relatively safe to touch this as it's usually GROUND but in other devices with HV, you should exercise caution.  It may be grounded but it doesn't have to be.