When citing a resource with a comment following the page number, e.g. [@Jones_2010, 20, my emphasis], the resulting LaTeX export is \autocite[20, my emphasis]{Jones_2010}. This causes BibLaTeX to treat the entire postnote as raw text without automatic inclusion of a style-dependent page prefix. So when using a citation style that includes e.g. p. before the page number, the final result becomes

See for example (Jones 2010, 20).

while it should be

See for example (Jones 2010, p. 20).

BibLaTeX requires using \pno in such cases in order to trigger the page prefixing manually where the postnote string is too complex for automatic inclusion. Therefore, Pandoc should export such a citation as \autocite[\pno~20, my emphasis]{Jones_2010}. Respectively \ppno should be used for a page range.

Pandoc 2.2.1 with the command:
pandoc --read=markdown --write=latex --output=FILENAME --biblatex --top-level-division=chapter --number-sections --standalone --table-of-contents --include-in-header=header-includes.tex --include-before-body=before-body-includes.tex --bibliography=zotero.bib
(Note that an input file is missing because I use pandoc-mode in Emacs)