Right, using [+pagetitle+] leads to no result, because Jot does not understand/recognize this placeholder and therefore replaces it with empty text.
Incorporating into Jot’s template a pagetitle that the comment is attached to consists of two parts: 1) obtaining the id of the page (it is kept in jot_content table), 2) fetching the pagetitle itself (kept in site_content table). However, this task is solveable within single statement -- you need to call Ditto in an appropriate place of your comment’s template:
[[Ditto? &documents=`[+comment.uparent+]` &tpl=`parent-doc-title`]]
The content of "parent-doc-title" chunk should be simply:
Important: [+pagetitle+] placeholder has to be separated from comment’s template into standalone chunk; do not try to place it within Ditto clause
&tpl=`@CODE:[+pagetitle+]`, because Jot will parse it and replace with an empty text prior it is accessed by Ditto.