This may be apparent
As far as I know, a WMS service can only get an image back, not features (no geometry, just the image). Without the images, you can't, obviously query it. So you cna set the layers you want to see, and then a bounding box, but not query the individual layers.
What you require is a WFS service which allows feature access; the following is cut and pasted from Esri:
Serving your data through a WFS service allows any application that can work with Web services to access geographic features from your map or geodatabase. Unlike the OGC Web Map Service (WMS) that returns an image of a map, the WFS service returns actual features with geometry and attributes that clients can use in any type of geospatial analysis. WFS services also support filters that allow users to perform spatial and attribute queries on the data.
ESRI WFS Services
Just got hold of a filter example with WFS:
<?xml version="1.0" encoding="UTF-8" ?>
<wfs:GetFeature xmlns:wfs="http://www.opengis.net/wfs" xmlns:ogc="http://www.opengis.net/ogc" xmlns:gml="http://www.opengis.net/gml/3.2" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:sfbdl="http://www.snowflakesoftware.com/osopendata/boundaryline" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:gmd="http://www.isotc211.org/2005/gmd" xmlns:gco="http://www.isotc211.org/2005/gco" xmlns:gss="http://www.isotc211.org/2005/gss" xmlns:gts="http://www.isotc211.org/2005/gts" xmlns:gsr="http://www.isotc211.org/2005/gsr">
<ogc:Literal>Southampton, Itchen Boro Const</ogc:Literal>
Which returns that object from a WFS server; here's a link to some examples:
WFS Query Examples