How to initialize var just outside of the scope when it holds LINQ query.

I want to pass the anonymous type variable "linq" to the method LinqToDataTable to get Datatable loaded with values of linq..If i do like 

case "Profession":

{

var linq=......;

DataTable dt=new LinqToDataTable(linq);

return dt.

}

it works fine..but outside of the scope i couldnt able to use linq as i dont know how to initialize var as empty...if i use

Iqueryable<> linq=null; i have to specify type inside <>..In my scenario wat i have to specify as type?????DataClassContext??

public DataTable GetSelectionListData(string type, string selected, string filter, string filterType)
        {
           
            DataClassContext db=new DataClassContext();
        
        //IQueryable linq=null;  // This is where the problem arise.How initialize query type linq to null
                  
           switch (type)
            {
                case "Alert Id":
                    {
                        if (filter.Length > 0)
                        {
                            if (filterType.IndexOf(";") > -1)
                            {
                                linq=--;
                            }
                            else
                            {
                                linq=---;
                            }
                            }
                        }
                        else
                        {
                            linq=---;
                        }
                        break;
                    }
                case "Order Status":
                    {
                        linq=--;
                        break;
                    }
                case "Profession":
                    {
                        linq=--;
                        break;
                   }                    }
                                           
           }
         
            DataTable dt = LINQToDataTable(linq);
            return dt;
             
        }
     
  public DataTable LINQToDataTable<T>(IEnumerable<T> varlist)
{
     DataTable dtReturn = new DataTable();

     // column names
     PropertyInfo[] oProps = null;

     if (varlist == null) return dtReturn;

     foreach (T rec in varlist)
     {
          // Use reflection to get property names, to create table, Only first time, others
         
          if (oProps == null)
          {
               oProps = ((Type)rec.GetType()).GetProperties();
               foreach (PropertyInfo pi in oProps)
               {
                    Type colType = pi.PropertyType;

                    if ((colType.IsGenericType) && (colType.GetGenericTypeDefinition()
                    ==typeof(Nullable<>)))
                     {
                         colType = colType.GetGenericArguments()[0];
                     }

                    dtReturn.Columns.Add(new DataColumn(pi.Name, colType));
               }
          }

          DataRow dr = dtReturn.NewRow();

          foreach (PropertyInfo pi in oProps)
          {
               dr[pi.Name] = pi.GetValue(rec, null) == null ?DBNull.Value :pi.GetValue
               (rec,null);
          }

          dtReturn.Rows.Add(dr);
     }
     return dtReturn;
}