What should i destroy?

[Titus Marcellus Scato]

As a nomad, what building in a newly conquered town should i destroy?

i mean, i destroy the Nomadic goverment all the time....

First, destroy the enemy government (built by an AI faction) if there is one.

Second, look at the barracks. If you can recruit troops from it, keep it. If you can't, destroy it.

Third, decide whether your tribe is going to migrate to the town, or leave the current population and culture in place and turn them into an Allied Client State with local regional units.

If you plan to migrate, then every building (except maybe wonders) that is not of your own nomadic culture should be destroyed. If there are buildings of your culture, but say 'Western Greek' after their name, that means they are of your culture but built by a tribe that used to be hostile - they are OK to keep, they can be upgraded later and the 'Western Greek' bit will go away when you do.

If you plan to leave the current culture in place, and build an Allied Client State (Nomadic version of Type IV Government) then keep all the buildings. Build Military Occupation, Indigenous Settlements, Allied Client State.

Note: You don't need to destroy an existing Nomadism unless you want to convert the town to Pastoralism.