if there is a more definite etymological answer to that question, I would be interested to hear it, too, because this may be the question Hokkien writers were (and are) most devided about.
In Taiwan this word is usually pronounced ê and the Ministery of Education system uses two different characters for that: 的 for the attribute particle and 个 for the classifier. However this distinction seems very artificial to me because it is made on the basis of Mandarin grammar (的 vs. 個). Therefore, I have also seen a lot of people just use one character (mostly 个) for both. As far as I know, Cantonese also uses the same word for the attribute particle and the general classifier, which sounds like ge in some tone (I don't know Cantonese :oops:) and may or may not be etymologically related to the Hokkien word. This word is written 嘅, simply by adding a 口 to the character 既 which I guess is pronounced in a similar way in Cantonese. This way of writing unknown Cantonese words by adding 口 to an existing character seems pretty common in Cantonese writing, but if you want more information on that, maybe you should ask someone who actually knows Cantonese :lol:). In any case, I believe 嘅 would be more suited to spell Hokkien ê/leh with because the Cantonese word spelt with it is a much closer cognate to the Hokkien ê/leh than with either 的 or 個. On the other hand, the character it is derived from, 既, doesn't seem to have much of a phonological connection with ê/leh (but then again neither do 的 and 個).