How do you remove Yahoo Search from Ipadpro?

Presumably you refer the search engine used by Safari? If so, you can select a different default search engine for Safari in iPad settings:

Settings > Safari > [Search] Search Engine - select your preferred search engine from the list

What app is it present in?

sometimes things like this are part of the settings of a specific app (like if a browser has ‘helpful’ shortcuts preinstalled.

You’d need to poke around in the settings for the app in question