an 1837 austrian encyclopedia claims that he took part in the battle, and a couple of fr/en 19th century encyclopedias mention him but seem to have just copied the austrian one
remember this would be at a time when he was still more or less a nobody, a local noble, not a hussite warlord, so his presence would not be far fetched
that alone is not particularly noteworthy
however, his signature and seal are missing from a document signed by some 500 other nobles and supporters of jan hus at roughly the same time, suggesting that zizka was out of the country
a minor tidbit is that zizka might have witnessed the effect of rough terrain on heavily armored formations there, a tactic he himself successfully employed a couple of times, most notably in the battle of sudomer
however, his name does not feature in the english accounting documents from the battle
and at the time of the signing of the aforementioned document, he might have been in the service of the king, meaning he might not have been able to sign it
and we also have way more reliable evidence of his other foreign exploits at grunwald, as in chronicles, records, mentions - as opposed to, well, nothing about azincourt
so the bottom line is that maybe, and it is a very big maybe, he was at azincourt
but even if he was, it would not have been a big deal by any means