Do i need permission to sell something in a place that is owned by someone (either public or private place) even though i dont see/know any rule in that place that prohibites someone doing transactions there?.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

It is impermissible for someone to use a place owned by another for trade without the owner's permission. This ruling applies whether the place is private like a house or public like a mall or marketplace, and whether or not the owner has explicitly stated that it is forbidden to use his property for such purposes. This is because merely entering someone else's property is impermissible without his permission, and a permission to enter it does not permit the one entering to use the property to conduct sale transactions therein.

Allah knows best.