Totally uncorroborated (anonymous source), I believe this looks like a UK journalist reporting this. Looks like the original article was in the "Express", so a so-called "Red Top" but it does not necessarily mean it's false.
Khashoggi killed over plans to expose Saudi chemical attacks
By Sheetal Sukhija, Big News Network
29th October 2018,
LONDON, U.K. - Over the last few days, a complicated diplomatic conflict has taken hold of a case involving a cold blood murder - in an attempt to shift the focus of the world from the criminal act to a possible punishment for those behind it.
Yet, amid vague proclamations to punish the murderers and bold statements vowing the deliverance of justice - attempts to understand the reasons that sealed the fate of 59-year-old veteran Saudi journalist Jamal Khashoggi seem to be lost.
On Saturday night, a shocking expose emerged in a report in the Sunday Express, that has possibly reversed the course of a complicated case, that has, over the last month, appeared to be unsolvable.
More: https://www.bignewsnetwork.com/news/258206796/khashoggi-killed-over-plans-to-expose-saudi-chemical-attacks
Okay, it is in this story, discussion of the use of chemical weapons in Yemen.
https://www.express.co.uk/news/world/1037378/Khashoggi-murder-news-saudi-arabia-chemical-weapons-useKhashoggi BOMBSHELL: Britain 'KNEW of kidnap plot and BEGGED Saudi Arabia to abort plans'
Marco Giannangeli, Diplomatic Editor
Intercepts by GCHQ of internal communications by the kingdom’s General Intelligence Directorate revealed orders by a “member of the royal circle†to abduct the troublesome journalist and take him back to Saudi Arabia.
The orders, intelligence sources say, did not emanate directly from de facto ruler Crown Prince Mohammad bin Salman, and it is not known if he was aware of them.
Though they commanded that Khashoggi should be abducted and taken back to Riyadh, they “left the door open†for other actions should the journalist prove to be troublesome, sources said.
The article talks about "chemical weapons" a few paragraphs down at link. Something to file away, in case, anything comes of this. Just hearsay for now, in turn, it would be a real blockbuster if true.