G Plan Fresco Vanity soild wood or veneer top?  

Photo
Post a photo. Someone here will be able to say by looking at it. Mirrored grain already puts the likelihood at 99%. If there is a piece of edge trim hiding the end grain, that is another strong indicator. And veneer has a distinctive grain pattern as well due to how to is cut from the log.

Love to
see a photo.
I agree with Leif. And:
Just because an end view of the top doesn't show a veneer skin on top, doesn't mean it isn't there. Veneers are often sanded to almost zero thickness.
But if you don't see the typical end-grain of solid wood, what makes you think it might be solid wood ?
What does the end of the panel look like ? Is it MDF or other wood composite ? Or is there a veneer edge on that end, as well ? If the former, is there a veneer on the bottom of the panel ? What does the bottom face of the panel look like ?
So many questions, so few answers . . . so far !

Veneer
It is veneer according to the photos I find on google.

Veneer
It'll be veneer.
Solid timbers were mostly only used for legs, arms, stretchers and handles on G Plan Furniture

Veneer
... definitely veneer.