For a deeper look into our DataScope Select SOAP API, look into:
Overview | Quickstart | Documentation | Downloads | Tutorials
Any time you want to find if and where a specific data item might be found, the best solution is to use the Data Content Guide. Open tab "Field Descriptions", and use a text filter on column D or E to display only the rows that "contain" a keyword that defines what you are looking for, in this case I'd use "expir" and "convention".
I have just tried that, and found that a Composite request can deliver a field called "Expiration Date".
There are several fields that contain the word Convention, most of them delivered by the Composite request (and 2 delivered by the Bond Schedules request), you would need to check their description to find the one that corresponds to your needs.
On this topic you might also find this tutorial section interesting.