Possibly an appliance repair person can match the faulty ignitor with the correct part without knowing the manufacturer of the cooktop. That part is usually a common piece used by many cooktops etc. If you can remove it the part number could help in your search.

There isn't a cupboard below the unit via which the bottom of it can be seen?

Do a picture search in Google.

I wouldn't worry about the cooktop brand. I'd try to match an igniter with one of the igniter photos on Amazon.

thank you all for the comments.

Yes Dan, I think I will have to call a professional

Dadoes, there is a built-in oven underneath (GE, doesn't match cooktop) and it's impossible to access the cooktop from below.

Moose, never thought about Google pic search. I did find some models that were very close but no cigar.

Do you know how old it is? When the kitchen was redone (or house built)? Might help.

It bugs me...it really looks familiar!

I have an electric cooktop but the trim package and knobs on your cooktop look almost identical to mine. It's a Viking and the logo is long gone after countless cleanings.  We're going to be replacing ours in the coming months as all four switches are shot and we were told by a repairman that the parts alone were $200 plus EACH not including labor.  Good luck.

What is that mark in the upper left hand corner near the olive oil bottle?

You guys are awesome! It is a Viking https://www.vikingrange.com/consumer/product/products/retired-models/retired-cooking-products/30--gas-cooktop---dgcu