Formal:
* ピアスをしています (ピアスをしております) (piasu wo shite imasu/imasu) - This is the most formal way to say it, using the present progressive tense to indicate that you currently have the earring.
* ピアスをつけています (ピアスをつけております) (piasu wo tsukete imasu/imasu) - This is another formal option, using the verb "つける" (tsukeru) which means "to put on" or "to wear".
Informal:
* ピアスしてる (piasu shiteiru) - This is the most common informal way to say it, using the present progressive tense in a casual way.
* ピアスつけてる (piasu tsuketeiru) - Similar to the formal version, but using the informal version of the verb "つける" (tsukeru).
To be more specific, you can say:
* 〇〇ピアスをしています (〇〇ピアスをしております) (〇〇 piasu wo shite imasu/imasu) - Replacing 〇〇 with the type of earring, such as "金" (kin, gold) or "ダイヤモンド" (daiyamondo, diamond).
* 〇〇のピアスをつけています (〇〇のピアスをつけております) (〇〇 no piasu wo tsukete imasu/imasu) - Same as above, but specifying the type of earring using "の" (no) which means "of".
Example:
* 私はピアスをしています。 (Watashi wa piasu wo shite imasu.) - I have an earring.
* 金ピアスをつけています。 (Kin piasu wo tsukete imasu.) - I'm wearing a gold earring.
Remember to use the appropriate level of formality depending on who you are talking to.