In your pushtopic definition you tell the server what fields to send

for my test environment.

select name,id, description__c from problem__c where .....

and I get a streaming event message

Received Message: {"data":{"sobject":{"Name":"123461","Id":"a0O30000009JhdcEAC","Description__c":"this is a test problem of a synchronized problem"},"event":{"type":"updated","createdDate":"2012-07-02T13:42:56.000+0000"}},"channel":"/topic/updatedProblem","clientId":"vxfsf6gvp04bu133otjrsh4g3y"}
id found=a0O30000009JhdcEAC

and so you can use the id field to  make further soql calls just like normal

( this is a test system)

so my soql back is

select name from Problem__c q where id='a0O30000009JhdcEAC'

and then I get the SF select response, and have to parse that as always.,

my streaming code is all in Java,  there is nothing on the server side except the pushtopic creation.

here is my streaming event message handler.

I parse the JSON response into a hashmap

and then access the hashmap

all of this is standard documented SF Partner WSDL apis. (and my creation of code using them)

			client.getChannel(CHANNEL).subscribe(new MessageListener() {
				public void onMessage(ClientSessionChannel channel, Message message) {
					System.out.println("Received Message: " + message);
					try
					{
					    JSONReader reader = new JSONReader();
					    Object result = reader.read(message.toString());
					    if(result.getClass().getName()=="java.util.HashMap")
					    {
					    	String id=getItem((HashMap)result,"data.sobject.Id");
					    	if(id!=null)
					    			System.out.println("id found="+id);
					    	String qs=f.replace(fakeid, id); // build the query string
					    	System.out.println("query string="+qs);
					    	QueryResult qr=connection.query(qs);  // call SF partner api to get more 
					    	System.out.println("there were "+qr.getSize()+" records returned");
					    	SObject[] recordinfo=qr.getRecords();  // get the select results
						    	// process the select results
						    	Iterator it=recordinfo[0].getChildren();
						    	while(it.hasNext())
						    	{
						    		processObject((XmlObject)it.next());
						    	}

						    	System.out.println("there are "+qr.getSize()+ " children");
					    }
					}
					catch (Exception e)
					{
						// TODO Auto-generated catch block
						e.printStackTrace();
					}