Boss Souls and Boss Respawn

Hi,

So, one of my questions is if I can gain the boss soul by kill bosses in other people world or just in my world?

And if i Kill the boss in my world and want to respawn him again How can i do it? Using bonfire astetic?

Thanks!

You only gain a boss soul in your own world. And yes, you need to use an Ascetic on the bonfire closest to the boss area to respawn it. Although this increases the difficulty of all enemies in the vicinity too.