• olacing on,
• llacing on,
• -lacing on,
• 0lacing on,
• pkacing on,
• ppacing on,
• poacing on,
• plzcing on,
• plscing on,
• plwcing on,
• plqcing on,
• plaving on,
• plafing on,
• plading on,
• placung on,
• placjng on,
• plackng on,
• placong on,
• plac9ng on,
• plac8ng on

The adverb form of "placing on" is "placingly".

The adjective form of "placing on" is "placing". However, if you are specifically looking for a word that describes something as being in the act of being placed on, you could use "placing-on" as a compound adjective. For example, "the placing-on process" or "the placing-on action".