A French term for the official record of negotiation, Travaux can help resolve ambiguities in the text itself and the intent of the parties.
Ideally, someone has already collected those materials and published them as a book, which is easily discoverable in a library catalog by using the French term itself as a keyword. For example:
The Travaux Prèparatoires of the Crime of Aggression by Some travaux like material has been compiled and is available online, like at the Historic Archives of the United Nations:
If neither is an option, then you are left to searching secondary sources for references to the necessary materials that you could then track down by citation.
Three things you will need to figure out to understand the current status of a treaty: 1) whether or not it has entered into force, 2) whether or not a country has become a party, and 3) whether or not a country has made any Reservations, Understandings, or Declarations (RUDs), which can impact the effect of the agreement.
To figure out whether a treaty has entered into force, it is easiest to go directly to the text of the treaty itself to see what conditions were required. This is typically found towards the end of the agreement.
To both figure out whether a country is a party and whether or not they have lodged any RUDs, your best bet is to look towards the Despositary Institution. For example, the United Nations, which serves as the depositary for many treaties has a database that will give you status information: