I want to know how an Oracle table (or column) knows which sequence is used or applies to that specific table (or column).
As far as I know, sequences aren't systematically associated with a particular table in Oracle. According to the documentation:
Without sequences, sequential values can only be produced programmatically. A new primary key value can be obtained by selecting the most recently produced value and incrementing it. This method requires a lock during the transaction and causes multiple users to wait for the next value of the primary key; this waiting is known as serialization. If developers have such constructs in applications, then you should encourage the developers to replace them with access to sequences. Sequences eliminate serialization and improve the concurrency of an application.
So the developers of the application need to associate each sequence with the table(s) they are used with. Usually this is done by using a name that somehow indicates what it's used for. So a sequence for populating emp table's primary key might be called emp_sequence.