Type in expressions to have them evaluated.
Type :help for more information.

scala> def foo[T]{
  import scala.reflect.runtime.universe._
  val tt = implicitly[WeakTypeTag[List[T]]]
  println(tt)
}
<console>:9: free type: Ident(TypeName("T")) defined by foo in <console>:7:16
         val tt = implicitly[WeakTypeTag[List[T]]]
                            ^
foo: [T]=> Unit

scala> foo[Int]
WeakTypeTag[scala.List[T]]

scala> :quit