First of all, I am going to suggest you need access to a copy of the Niagara N4.7 Developer Workbench (unless you already have this ?).
Once inside the workbench, there are two specific pieces of documentation inside the Workbench Help which might assist you. The first is docDeveloper, which gives you a complete guide for developing Niagara components. The second is by searching for 'oBIX' in the Help Search toolbar; this will list lots of items relating to oBIX, but the best one to read first is 'NiagaraAX oBIX Guide'.
I should also mention that there is an oBIX driver already written and available in N4. I don't know your exact circumstances, but perhaps you could use that ?
Hope this helps.