There is no good way really.
Lemmy’s search is pretty lackluster. You will have a hard time finding what you are looking for, unless you are searching for something verbatim, and if your query contains common words…Good luck. It also has no search operators.
When it comes to search engines, only google is somewhat usable (from my experience), but it’s very much hit or miss. Sometimes you will be able to find the post, just by typing lemmy [post title or part of it], but it will almost never be in the top results.
And most of the time , first result is Reddit…
It basically just uses this query for “more accurate search” [search query] (intext:“modlog” & “instances” & “docs” & “code” & “join-lemmy”)
And this one for normal search [search query] (site:lemmy.world OR site:lemmy.ml OR site:lemm.ee OR site:hexbear.net OR site:sh.itjust.works OR site:lemmy.dbzer0.com OR site:feddit.de OR site:kbin.social OR site:mastodon.social OR site:mastodon.cloud OR site:mstdn.social OR site:mastodon.online OR site:mastodon.world OR site:libre.video OR site:video.antopie.org)
Which is not just for lemmy, as you can see
Here is the search query I made for the top 35 lemmy instances (by active users) based on this: lemmy.fediverse.observer/list
<span style="color:#323232;">[your search query] (site:lemmy.world OR site:lemm.ee OR site:sh.itjust.works OR site:lemmy.ml OR site:hexbear.net OR site:lemmy.ca OR site:programming.dev OR site:lemmy.dbzer0.com OR site:feddit.org OR site:lemmy.blahaj.zone OR site:discuss.tchncs.de OR site:lemmygrad.ml OR site:sopuli.xyz OR site:lemmy.sdf.org OR site:lemmy.zip OR site:beehaw.org OR site:infosec.pub OR site:aussie.zone OR site:feddit.nl OR site:midwest.social OR site:feddit.uk OR site:slrpnk.net OR site:reddthat.com OR site:lemmy.one OR site:jlai.lu OR site:pawb.social OR site:lemmy.kya.moe OR site:lemmy.today OR site:startrek.website OR site:feddit.it OR site:mander.xyz OR site:ttrpg.network OR site:lemmings.world OR site:ani.social OR site:feddit.org)
</span>
In SearXNG u can use !lepo to search lemmy posts but it’s basically just lemmy’s search.