Would the singular form of "tenaza" ever be used?
If you are saying "Where are the pliers?" or "Where are the tongs?" Can you only say ¿Dónde están las tenazas? or can you also say ¿Dónde está la tenaza? Is "tenaza" singular even a word?
Tenaza/s is both singular & plural. Tongs, for culiary things, etc.
Pinza/s is also both singular & plural, but used as mostly plural. Pliers for mechanical & hardware things.
When you look for these types of words in a dictionary, you have to look under the singular variant and then you are given the plural form if it exists.
I don't think that is the singular form of the word, because sometimes, words with an 's' on the end aren't plural. In this case, I think pliers/tongs would apply, because generally, the word plier/tong is not used. Hope I helped!
Ignoring the plural vs. singular issue, you could say "dónde se quedan las tenazas?"¿