I do not recall having any information about John so I suspect the information you have here might be all new to me. Do you have any sources for this that I might be able to pursue?
I also know nothing about him being an 'Architect'. In fact in my records which I think come from the Census I have him as an 'Artist'.
CT
That he was an architect is recorded in this ad from 'Cornishman' 10 Aug 1893. page 1 col 1.
"Tenders.
TENDERS are invited for the erection of a NEW
INFANTS' SCHOOL, to enlarge the present Board-
school at Sennen; the plans, specifications, and condi-
tions of which may be seen at the address written below.
SEALED TENDERS must be sent to the undersigned on
or before Thursday, August 24th, 1893.
The lowest, or any, tender will not necessarily be ac-
cepted.
(Signed)
JOHN TREWHELLA, jun., architect.
Sea-view-house, S. Sennen, Land's-end."
Sea View house is the residence of his father, shown on other records.
The 1891 census does list his occupation as "Artist". I don't whether he described himself as such then, or whether the Ennumerator mistranscribed the household sheet into the book he returned.
Another notice in "Cornishman" reports that he died in Africa.
10 October 1895, page 5, col 1
"Death of a young Sennen man in Africa.-
The many friends of Mr John Trewhella, of Sennen, will
be surprised to hear that from Africa has come the sad
tidings of the death of his son. John Trewhella, who only
left a month or two ago. Great sympathy is felt for the
family. Mr J. Trewhella, jun, it will be remembered,
was clerk of that parish for many years. But Africa had
greater attractions than the clerkship of Sennen."
If you would like a pdf copy of the whole page of these, happy to send by email.
Thanks for the other info in your post.
Simon