i have been working on a dk tank and i have got is so im def caped and been farming hcs for emblem of triumph but apart from def cap im not sure what im doing stats wise any help would be much appreciated
Yes, the defense minimum is your first priority. After that, you need to find a good balance of threat and survivability (for the content that you're doing). Going by your gear I assume you're doing heroics mostly, so I'll base my suggestions around that.
Your spec looks OK, I wouldn't put those two filler talents in Hungering Cold and Endless Winter, but rather Merciless Combat (which is at least somewhat useful), but that's pretty minor. Your glyphs make no sense though - Death Grip glyph is worthless for PvE, Dark Command is OK but not that crucial for heroics IMO, and why Bone Shield when you're Frost?
I'd change them to Obliterate (20% more threat on one of your main threat generators), Rune Strike (10% crit on your #1 threat generator), and Howling Blast (good for AoE pulls). I wouldn't recommend using single-disease Howling Blast rotation on bosses, because the second disease can definitely make a big difference in how hard your Obliterate and Blood Strike hit, but it's wonderful for AoE pulls. Throw down DnD on top of the mobs, use Howling Blast, and you still have a rune left over for a Blood Boil - really makes heroic tanking a lot easier.
For gear, you desperately need to replace that FR chestpiece. The extra defense afforded by a tanking chestpiece would allow you to gem more stamina, and the strength would give you more threat. I would consider this chest to be a solid upgrade. Frost resist pieces are for gimmick frost fights.
Other than the chest, you seem to have a good grasp of what stats to go after. Stamina is your #1 priority as far as staying alive, within reason - for example, this helm is better than this one even though the latter has higher stamina. Expertise, hit, and strength are your threat stats, and are what you want to go after if you're having threat issues (as you likely will in the new LFG system, where overgeared DPS are looking for a quick 15-minute roflstomp and are often unwilling to give a new tank time to generate aggro before going all-out).