The value property of the slider is an array, which contains both the value. You just need to populate the values in two different inputs instead of one. like below
require(["dojox/form/HorizontalRangeSlider", "dojo/dom", "dojo/domReady!"], function(HorizontalRangeSlider, dojoDom){
var rangeSlider = new HorizontalRangeSlider({
name: "rangeSlider",
value: [2,6],
minimum: -10,
maximum: 10,
intermediateChanges: true,
style: "width:300px;",
onChange: function(value){
dojoDom.byId("sliderValueMin").value = value[0];
dojoDom.byId("sliderValueMax").value = value[1];
}
}, "rangeSlider");
});
<link href="//ajax.googleapis.com/ajax/libs/dojo/1.11.2/dijit/themes/claro/claro.css" rel="stylesheet"/>
<link href="//ajax.googleapis.com/ajax/libs/dojo/1.11.2/dojox/form/resources/RangeSlider.css" rel="stylesheet"/>
<script src="//ajax.googleapis.com/ajax/libs/dojo/1.11.2/dojo/dojo.js"></script>
<body class="claro">
<div id="rangeSlider"></div>
<p><input type="text" id="sliderValueMin" /></p>
<p><input type="text" id="sliderValueMax" /></p>
</body>