We build the dialog outside the repeat control and then the action that launches or shows it also sets a viewScope variable that is used UNID for the data source in the dialog. Just make sure you refresh the contents of the dialog as you open it...
<xp:view xmlns:xp="http://www.ibm.com/xsp/core" xmlns:xe="http://www.ibm.com/xsp/coreex">
<xp:this.data>
<xp:dominoView var="promptView" viewName="dlgBoxes">
</xp:dominoView>
</xp:this.data>
<xp:panel>
<xp:repeat id="repeat1" rows="30" value="#{promptView}" var="promptEntry">
<xp:panel tagName="div">
<xp:text escape="true" id="computedField1" value="#{promptEntry.dlgName}">
</xp:text>
 
<xp:button value="details" id="button1">
<xp:eventHandler event="onclick" submit="true" refreshMode="complete">
<xp:this.action><![CDATA[#{javascript:
var pe:NotesViewEntry = promptEntry;
viewScope.put("dlgDocUnid", pe.getUniversalID());
getComponent("dialog1").show();
}]]></xp:this.action>
</xp:eventHandler>
</xp:button>
</xp:panel>
</xp:repeat>
</xp:panel>
<xe:dialog id="dialog1" keepComponents="false" partialRefresh="true">
<xe:this.title><![CDATA[#{javascript:
var unid = viewScope.get("dlgDocUnid");
if(!unid) return "";
var doc:NotesDocument = database.getDocumentByUNID(unid);
return doc.getItemValueString("dlgName");}]]></xe:this.title>
<xp:panel>
<xp:this.data>
<xp:dominoDocument var="dlgDoc" formName="dlgBox" action="openDocument">
<xp:this.documentId><![CDATA[#{javascript:viewScope.get("dlgDocUnid");}]]></xp:this.documentId>
</xp:dominoDocument>
</xp:this.data>
<xp:text escape="true" id="computedField2" value="#{dlgDoc.Title}">
</xp:text>
<xp:br></xp:br>
<xp:br></xp:br>
<xp:text escape="true" id="computedField3" value="#{dlgDoc.dlg}">
</xp:text>
</xp:panel>
</xe:dialog>
</xp:view>
Happy coding
/Newbs