value vs knob command

The simplicity of tcl's command based nature makes it nice and easy to use in Nuke's text knobs, such as labels (you can actually use tcl that way in pretty much any knob in Nuke that can take an expression).
The value and knob commands in particular are very handy to show node properties in the DAG.
In a node's label, simply type the following:

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[value <knob name>]

Here is an example for the exposure node's "mode" knob:

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[value mode]
rgb: [value red], value green], [value blue]

Note that the "value" command will resolve any expressions or animation curves for you, and return their respective current value.
If you want to get the literal content of a knob without prior resolution, use the "knob" command instead:

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[knob <knob name>]

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[knob rotate]