If you're hunting for the official source of 'Solo Leveling', the clearest place to start is the original Korean web novel release — it was published on KakaoPage under the author Chugong. That's the canonical text that the manhwa adapts from, and if you can read Korean or want the unabridged original, KakaoPage is where it lives. There are also official printed volumes in Korean, so retailers that carry Korean books (like YesAsia, Kyobo, or Korean online bookstores) will have legitimate editions if you prefer physical copies.
For English readers, the situation is a bit different: there hasn't been an official, complete English release of the light novel text itself. The best legal way to enjoy 'Solo Leveling' in English is the officially licensed manhwa, which is available on platforms like Tappytoon and KakaoPage's global service, and those releases support the creator and the original publisher. If you're set on novel-format reading, keep an eye on announcements from publishers and major ebook stores — sometimes licenses get picked up and English volumes appear on Amazon Kindle, BookWalker, or publisher storefronts. Personally, I check publisher socials regularly to catch any official translation news; it’s how I avoid sketchy scans and still get my fix while supporting the creators.