You can build an expression tree which contains accessing a given field by its name using Expression.Field method. For example, you have the following code.
TestClass obj = new TestClass();
Console.WriteLine(obj.myField);
Here is the code that is required to build the same functionality using expression tree.
Expression fieldExpr = Expression.Field(
Expression.Constant(obj),
"myField"
);
Console.WriteLine(Expression.Lambda<Func<int>>(fieldExpr).Compile()());