public static XPQuery<T> Query<T>(
    this IDataLayer layer
)

<ExtensionAttribute>
Public Shared Function Query(Of T)(
    layer As IDataLayer
) As XPQuery(Of T)

using System.Linq;
using DevExpress.Xpo;

// ...

var data = from c in session1.Query<Person>()
           where c.LastName.StartsWith("A")
           select c;

'NOTE: This code snippet uses implicit typing. 
'You will need to set 'Option Infer On' in the VB file or set 'Option Infer' at the project level:

Imports System.Linq
Imports DevExpress.Xpo

' ...

Private data = from c in session1.Query(Of Person)() where c.LastName.StartsWith("A") select c