Based on technical data analysis, there is a short list of candidates, which potentially could become supernova; in fact, one may have done so already! 

There are a cluster of about 150 stars called the Arches Cluster, which bear multiple supernova prone characteristics, located at: 17h 45m RA and -28h 49m Dec, near the Galactic Center.  This collection of stars each bear all characteristics or extreme critical values that should put them way over the top as a supernova compelling, imminent eruption.  They are in our galaxy and form a localized class of highly favorable conditions for the event.  However, we do not know much about the individualized environments (planets, binary affiliations, local neutrons stars, nor loose black holes in the area), so no definite star can be singly identified as the next in line to go supernova. 

Estimates of likely supernovas usually include Betelgeuse. In a very local star,  SN progress could be monitored and documented by the flares and changes in radii. However, Betelgeuse presents some serious physical conditions, which this author proposes, prevents a rapid unfolding to an immediate supernova demise. First, Betelgeuse’s temperature seems too low to immediately trigger an irreversible supernova mode according to standard models.  The star would need to ascend into rapid heating to place in a suitable position on the Hertzsprung-Russell Diagram.  Secondly, it has a planet and maybe two planets.  The effect of any satellite on the progress of a body that had run out of fuel is unknown.  Based on pulsar inspiral paths and wayward stars seen ejected from the Milky Way galaxy, anything could happen.  What are the cut offs here? The final and relevant question then becomes, when will Betelgeuse become a supernova?  My answer: it should not begin to start until its thermal temperature reaches at least 30,000K. This may be very rapid, only taking place over hours, weeks or months when it does begin.  Betelgeuse is one of the most visible and easily measured stars in the night sky, visit SNBetelgeuse.com for further observations of a really bright star, before and monitor it as it goes supernova, at roughly 500 LY away.

Lets move on to the highest priority candidates.  The following stars (in no particular order) have one or more indicators which hallmark an immediate and super-major supernova event, destroying the entire existing star structure and creating either a black hole or neutron star :

Cygnus X-1:      14-16 solar masses; temperature 31, 000K; luminosity 3-4 x 105

W Cephei A/B:   25/20 solar masses; temperature 3,800/25,000K; luminosity 2-3,2 x 105/104

R 136a1:            265 solar masses; temperature 53,000K; luminosity 8.7 x 106

WR102ka (Peony Star):  175 solar masses; temperature 25,100K; luminosity 3.2 x 106

HD 269810:       150 solar masses; temperature 52,000K; luminosity 2.2 x 106

VFTS 682:         150 solar masse; temperature 52,200K; luminosity 3.2 x 106

HD 93129 A/B:  25/80 solar masses; temperature 52,000K/- ; luminosity 3.2 x 106/ 106

Rigel A:              18 solar masses; temperature 12,130K; luminosity 1.26 x 105

Canopus:           9-10.6 solar masses; temperature 7,350K; luminosity 15,100

Pistol Star:         80-150 solar masses; temperature 11,800K; luminosity 1.6 x 106

Eta Carinae A/B: 120/30 solar masses; temperature 15,000/37,200K; luminosity 5 x106/106

Rho Cassiopeiae: 14-30 solar masses; temperature 6500-7200K; luminosity 5 x105

Alnitak:               28 solar masses; temperature 30,000; luminosity 105