[v] How can I find out whether a State has made reservations or declarations in relation to a particular Hague Convention?

Click on Conventions, choose the Convention you are interested in, and click on "Status table" in the right-hand navigation menu.
The column "Res/D/N" (= Reservations, declarations, notifications) provides a link to the relevant information for that State, which also shows the articles under which the reservation or declaration has been made.