Rather than using

container[i].name == 'lblQuestionType'

you will need to pass the ClientID property of the label into your javascript function and test against the id not name property which may not be present.

Take a look at the source html being generated for your page and you will see what is being used for the name (if present) and the id attributes of the span.

What Bill say that you can view the source file and try looking for the label id name.

I even find a better way, if you lazy to find the id in the source code. On your javascript you can use this

if  ( container[i].name.indexOf('lblQuestionType')>0){

//perform your action here
}

The drawbacks is you have to use a for loop.

Another quick solution: you can declare a variable for javascript in the page load
something like this

lblScript.Text = " var labelID = '" & lblQuestionType.Text & "'"  (this is only partial codes)