I have a 2005 Ford F-250 where is the best place to ground brake wireon a N2?

I assume it's any chassy ground, also once I ground it (I have already done the "pen" bypass) I don't have to re ground it everytime I use it do I.

any ground will work. might want to put it with other grounds though.

where does the speed sensor wire go?

I believe its on the radio wire harness. grey / black maybe

Yup gray/black at the radio harness.