Note that starting with Version 5.12, there will be extension methods that allow getting property values already casted to proper datatype. This will allow making code like yours be written in a shorter way.

I have prepared two examples
The first example obtains the data type through OPC property:
// This example shows how to obtain a data type of an OPC item.

using System;
using OpcLabs.EasyOpc;
using OpcLabs.EasyOpc.DataAccess;

.....
var easyDAClient = new EasyDAClient();

// Get the value of DataType property; it is a 16-bit signed integer
var dataType = (short)easyDAClient.GetPropertyValue("", "OPCLabs.KitServer.2", "Simulation.Random",
DAPropertyId.DataType);
// Convert the data type to VarType
var varType = (VarType)dataType;

// Display the obtained data type
Console.WriteLine("DataType: {0}", dataType); // Display data type as numerical value
Console.WriteLine("VarType: {0}", varType); // Display data type symbolically

// Code below illustrates how decisions can be made based on type
switch (varType)
{
case VarType.R8:
Console.WriteLine("The data type is VarType.R8, as we expected.");
break;

// other cases may come here ...

default:
Console.WriteLine("The data type is not as we expected!");
break;
}
.....
The second example reads an item and interprets the data type of the item value:
// This example shows how to read a single item and obtains a type code of the received value.

using System;
using OpcLabs.EasyOpc.DataAccess;

.....
var easyDAClient = new EasyDAClient();

DAVtq vtq = easyDAClient.ReadItem("", "OPCLabs.KitServer.2", "Simulation.Random");

TypeCode typeCode = Type.GetTypeCode(vtq.Value.GetType());

Console.WriteLine("TypeCode: {0}", typeCode);
.....

If you want to get that information before you actually operate invoke some reading or writing on the tag, you can use the GetPropertyValue method, passing in DAPropertyId.DataType. You will get back one of the constants defined in VarType type.
If you have read the value already and want to figure out what it is, there are multiple ways how to do that. You can e.g. do .GetType() on the value and then compare it to a specific type, such as typeof(int), or do Type.GetTypeCode(value.GetType()), and then compare it to one of the TypeCode enumeration members (ms-help://MS.MSDNQTR.v90.en/fxref_mscorlib/html/ec83d2c5-2704-dbbc-4fdb-ac5759b7940e.htm ). You can also use the 'as' operator to try cast the value to what your code actually needs.