Can someone help me with Pokemon's IV?!

Imagining two dragons one 15/15/15 and other 15/0/0 (att/def/hp), with the same moveset and CP they will do a similar damage. But the poor ivs one will be like level 40.5 when the 100% will do the same work in level 32 (just a example).

same CP =~ same efficiency ;-)

if you really want to do in the detail must calculate everything, this is not always accurate because even for a PC there are several posibility to IV and level.

i think at same CP the worsted IV win the fight.
because you dont use the same CPM when calculated stats

https://pokeassistant.com/main/ivcalculator?locale=en
You can check PokeAssistant to see how your pokemon's IVs affect its Atk, Def, and Stm stats.

IVs affect how high a pokemon's stats can get if you are powering it up as high as possible, and by extension how high its CP can get for gym placement.

Each IV will be added to the pokemon's base stats. A 0% Dragonite would have:
ATK 250
DEF 212
STA 182
A 100% Dragonite will have:
ATK 265
DEF 227
STA 197
So yes, a 100% Dragonite would not just make more damage, but will recive less damage and have a higher HP than a 50% Dragonite (assuming that none of its stats are 15)