I bought 2 small cubes from my friend for $50 and he just gave me the dual jewel cubes, but on the back its not a normal plug and its not labeled, which side is positive and which is negative?

I don't think it matters, as long as you have the same terminals on both receiver and speakers as "+" and ditto for "-".

bose cubes have no electronics or crossovers in them. thats why they run out of the bass module.

in short, they arent supposed to be connected to an amp directly in the first place.

Similar question, on the module RCA output, if an RCA male-male plug is used, is the inside plug + or - ?

well if you are really set on using them like that, it would just require the original cable and a continuity meter

Typically on an RCA male plug, the center pin is hot +

it will run through a crossover and my denon receiver will also know its a small speaker too

OH!, i forgot, its a JEWEL CUBE, not the regular big cube, if you look here on PAGE 12

http://www.bose.com/pdf/customer_service/owners/ig_ls_dvd_systems.pdf

thats the plug i'm talking about, its not an rca end and i dont have the original wires, it just has a plug with 2 metal poles inside and a notch at the top, unmarked of course so i need to know which side (looking at it) is +/-

You're wasting your time and are going to be disappointed. The frequency response of those cubes doesn't extend low enough for them to be useful without the bass module. There is going to be a huge gap from the crossover frequency up to what ever frequency those cubes start having any useful output. Enjoy your new paper weights.

I bought 2 small cubes from my friend for $50 and he just gave me the dual jewel cubes, but on the back its not a normal plug and its not labeled, which side is positive and which is negative?

I see a project......
$50 for something you may not be able to use ? I hope he's enough of a "friend" to get your money back. Rather than straight from a receiver, as a project I'd do an 8" dual VC passive sub ,use existing old speaker box, with a 150 to 200 hz commercial crossover for $50 max total. I'd also call Bose to get their sensitivity rating as match for the sub driver (guess is 85-90 db)...Bose sells adapters for speaker wire to rear plug ins. Don't expect anything special as they are made as part of an entire 5 speaker system and just two will have limited use....as did the entire system. It won't really be a sub woofer in passive form, but will extend the range of those jewel cubes for full range speaker. But, they could surprise and make a decent bedroom stereo unit.
Altenative would be to use a single vc woofer with less than 85 db sensitivity, and series wire the jewel cubes at the output, and hope for the best as a CC speaker. How good a friend is he ?

Always negative ;)