hi XX ! it Depends on your project type & your role in the project
what i try to understand first
.Understanding data model , understanding measures and dimensions helps in quick understanding of business requirements and saves a lot of time while developing
.Naming conventions and vocabulary ,connection paths,file structure
.first give importance in understanding on going work/half done work
.Don't forget to ask what is most demanding task in his opinion that will tell you where you should be focusing more energy
.Don't hesitate to ask admins what is the right time to schedule your tasks or about your access privileges
and list goes on depending on your role. Every organization will have its own way of achieving objective's don't be shy in asking details
