The structure of WKT was originally defined in the standard OpenGIS® Implementation Standard for Geographic information - Simple feature access - Part 1: Common architecture https://portal.ogc.org/files/?artifact_id=13227. The current version of the standard is https://portal.ogc.org/files/?artifact_id=25355 and that is used as reference below.
EDIT
Excerpt from 7.2.1 BNF Introduction (bolding added):
The text representation of the instantiable Geometry Types implemented shall conform to this grammar. Well known text is case insensitive. Where human readability is important (as in the examples in this standard), an “upper camel-case” where each embedded word is capitalized, should be used
One can also try to interpret the BNF definition. In WKT geometry names point, linestring etc. are "names". "Name" is made of "letters", "letters" are made of "simple Latin Letters", which are made from a set of small case and upper case letters.
<name> ::= <letters>
<letters> ::= (<letter>)*
<letter> ::= <simple Latin letter>|<digit>|<special>
<simple Latin letter> ::= <simple Latin upper case letter>
|<simple Latin lower case letter>
<simple Latin lower case
letter> ::=
a|b|c|d|e|f|g|h|i|j|k|l|m
|n|o|p|q|r|s|t|u|v|w|x|y|z
<simple Latin upper case
letter> ::=
A|B|C|D|E|F|G|H|I|J|K|L|M
|N|O|P|Q|R|S|T|U|V|W|X|Y|Z
Thus Point and POINT are both OK, and nothing wrong with poinT either.