I went to pick up my son from playschool.
There were lots of shoes on the shoe rack.
I asked my son,
"Which one is yours?"
"Which shoes are yours?"
Can one used for shoes since there are two items.
As the subject shoes is plural, you should use ones as such.
Which ones are yours?
If you were asking about a particular singular shoe or item, then
Which one is yours?
would be correct.
You can assume shoes come in pairs, and can use:
Which pair of shoes is yours?
or simply:
Which pair is yours?
where it is assumed you are talking about shoes.
Pair is defined as (Google):
a set of two things used together or regarded as a unit
and hence takes the singular form of the verb.
