15 percent of the full turn meter. So if their turn meter was at 60 percent at the time HK cast her ability, it would jump to 75 percent immediately. If it was at 85 percent, it would jump to 100 percent immediately and they'd get their turn immediately after HK - possibly jumping ahead of opponents who would otherwise have taken their turn faster. 

Some abilities may place debuffs on opponents without any actual attack. Then you will never do any damage with that ability, but only put the debuff - assuming you have high enough accuracy to beat the opponent's resistance. Those abilities also have the advantage that you can't have a weak hit which automatically fails to put the debuff - weak hits are only possible for actual attacks, against people of the affinity against which you're weak, not for debuffs that are just placed without any attack. 

As for damage based off attack/def/hp: for most champions, damage is based on attack - but of course they also need enough def/hp to survive. Depending on the type of champion and on how you want to use them, you may still prioritize def and/or HP even on a champion whose abilities scale off attack, for instance when it's a support type champion whose damage output is really unimportant compared to their support skills. For the minority of champions whose damage scales off defense or HP, that means they are easier to gear because then you can actually ignore attack as much as possible, pushing everything into def / HP. 

when a battle starts, what is the level of turn meter by default for each champion? speed and turn meter is different because turn meter will not increase your speed, is that correct to say?

resistance cancels accuracy in opponents. is that correct to say? 

for example in mountain king the damage is based on hp, so hp should be first priority, i have seen video where MK had 110k hp, does that mean his attack would be deadly?

similarly, soulbound boyer says reduce turn meter completely, which is supposed to better than coldheart. so if i have both soulbond and coldheart , i shud be able to keep spider and fire knight down quite easily.

when you say debuff on enemy champ without attack, for example spirithost, in that case spirit host will forgo a turn , that is it will not attack but simply cast debuff.

Turn meter starts at zero for each champion, it's their speed that determines how quickly the TM fills. So the champion with the highest speed on either team will get the first turn and after that, if nobody manipulates speed or TM in any way, everybody will just take turns in order of their speed. Although if e.g. one champion has a speed of 200 and the other has just 95 speed, then the first champion will take already their second turn before the slow champion's first turn. 

Now if a champion boosts his team's speed, or decreases the opponent team's speed, it means they will gain turn meter at a faster/slower rate, starting from their current turn meter position. If they boost turn meter or reduce the opponent's team turn meter, it means their current turn meter position moves forward/backward, but the rate of increase doesn't change. And some champions, like HK or Apothecary, do both things at the same time, boosting speed AND turn meter. 

Yes, resistance increases the accuracy that opponents would need to put debuffs on you. If your resistance is much higher than your opponent's accuracy, they will almost always fail to put the debuff - however, there is a small chance of like 3 percent that they will put the debuff, even in extreme cases (e.g. even if you have 500 resistance and they have 50 accuracy). The other way around, as well; even if you have 50 resistance and they have 500 accuracy, there is still a +/- 3 percent chance that you will get lucky and resist the debuff. 

In MK, pushing his HP high is important, but don't forget his crit rate and crit damage - and obviously his speed, like on all champions. 

Coldheart is perfect for Fire Knight especially, because not only does she have Heartseeker, but she has a 4-hit A1 with heal reduction. In Spider, her turn meter reduction is not necessarily much better than Soulbond's, but the difference is that CH will do massive damage with that ability, at least in the high stages, because it scales off enemy max HP. 

As for Spirithost, I think you need to reread her abilities. She doesn't put any debuffs on opponents, she removes the debuffs on her allies and prevents any other debuffs from being placed for the next turn. Debuff without attack includes abilities like Madame Serris' Midnight Ritual, for instance. 

As i understand it,,, the speed dictates how fast your turnmeter increases. HK and soulbound needs Accuracy to apply debuff, so u wanna build them up with acc. 

Do not underestimate debuffs - they are worth the turn (eg. spirithost). If a champion have no skill depending on attack u should COMLETELY forget all about attack. However attackchamps can benewith from DEF and HP. In general that makes att-based champs fragile, but usually they deal more damage and will benewith a lot from increase att boost or decrease def debuff.