You are trying to obtain data in the fields of Marketo Custom Objects, but you are unsure where or how to access this data.
There is not a location in Marketo that has an option to export Marketo Custom Object data.
Smart lists will show a list of leads with that specific attribute, and you can see custom object data on an individual Marketo record.
However, using API, you or your dev team can query the Marketo database to access all values on these objects. Find out more at Custom Objects.