The computer engine code P0308 means that the vehicles computer has detected that the number 8 cylinder is not firing and has a misfire.
It could mean that a spark plug is bad, ignition coil could be bad or something could be wrong with the cylinder itself.
Another possibility is that low fuel pressure could be causing a certain cylinder to misfire.
I would take it to a shop who can do a more diagnostic test to find out the exact cause of the cylinder misfire on number 8 cylinder as it can be caused by a number of different things.