You can only use the UNICODE or LATIN character sets with the JSON data type. Other character sets such as GRAPHIC, KANJI1, or KANJISIS are not supported.
In each particular use of the JSON data type, you can specify the character set using the CHARACTER SET clause. If you do not specify a character set, then the default character set for the user is used.
Character Set Handling
The JSON data type accepts all available session character sets. The data is translated to either the UNICODE or LATIN character set, depending on the definition of the JSON type instance where the data is being used. Therefore, any characters used must be translatable to either UNICODE or LATIN.
Any character set that must be translated is subject to the size restrictions of the UNICODE or LATIN character set. The data in some character sets may appear to be the correct size, but when translated to one of the two character sets, the data may be too large and result in a size error.
If the data transformed from a JSON instance needs to be in a particular session character set, the database will perform the translation, assuming that all of the characters can be translated to that character set.