"He is the engineer."
Translation:Is é an t-innealtóir é.
You do need it, actually. Unless you're speaking Ulster Irish. You can drop them both, however, and use eisean.
http://www.nualeargais.ie/gnag/kopul5.htm#bestimmtes Prädikat (ctrl-f "He is the" for the relevant section).
So you can have:
Is é an t-innealtóir é (Standard) Is é an t-innealtóir (Ulster Irish only) Is eisean an t-innealtóir (Perhaps more colloquial, emphasis form)
I still have no idea what you mean when you talk about this "copula" and I'm very well educated... I thought. I have no clue what the copula is and when to know it's involved or why it matters. I'm beyond frustrated, thinking there's no hope for me with Irish. Physics is easier than Irish!