I dont know how to find a DC and what kind of skills or spells i can use to found properties of an item magic
For instance i have a Magical Ring +1 Natural AC, what is the DC to discover this property on the ring and what skill i have to use to detect it ?
Are you playing Pathfinder 1st edition or the Pathfinder 2nd ed playtest? (If you don't know which you're playing, it's the former.)
If you're playing Pathfinder 1st edition, then
1) You'll usually use the detect magic cantrip on the item for three rounds and apply the Spellcraft skill against a DC of (15 + the item's caster level).
The item's caster level should be listed in its entry in whatever source your GM got it from. If the GM made up the item, they get to make up its CL too, generally by comparing to similar items.
The identify spell does the same as detect magic, but with a +10 on the Spellcraft check.
2) You've gotten onto the wrong subforum; this one is for the playtest, so you'll want to direct any follow-up questions to Rules Questions.
If you're playing the playtest, then you want the Identify Magic action for the Arcana, Nature, Occultism, or Religion skills (pages 145, 153, 154, 156 respectively). This takes a full hour ten minutes (there was an update) per item (less if you have the Quick Identification skill feat). I can't figure out how to find the DC for an item (as opposed to a spell, which there's a table there for) at all, unfortunately, so hopefully someone else will chime in. :-(
I believe the suggested identify baseline was a hard DC of the item's level. I shifted that down to a medium in my own games because with the amount of magic items pathfinder hands out identifying them shouldn't be that big a deal.
I also ruled arcana is the baseline skill that you can use for most items, but other skills might be used for related items. Occultism for mental magic, religion for healing items, nature for things like Verdant Staffs.