It depends whether you want it to be a static connection or a dynamic modulation routing.
If static, then a control.pma node would be the best candidate - connect the UI knob to the value and the envelope output (either from an extra_mod or an inbuilt scriptnode AHDSR) to the add output, this will combine the two with unipolar modulation mode.
Scales and offsets a normalised modulation signal using a multiply-add formula with clamped output.
The PMA node (Parameter Multiply Add) scales and offsets a normalised modulation signal. It takes a 0-1 input value, multiplies it by a configurable factor, adds a constant offset, and clamps the result to the 0-1 range. This is one of the most commonly used control nodes for adjusting modulation depth, inverting signals, or combining parameters.Each parameter change triggers an independent output update. If Value, Multiply, and Add all change in sequence, three separate output values are sent to connected targets.

