Мне не хватает только тех (людей), кто сейчас сидят на складе.
I need only those (people) who are sitting at the warehouse.

У меня нет того (той вещи), что сейчас лежит наверху.
I have no that thing, that is laying at the top.

in Russian we can use "that" for description as that/this.
And we can use it for replacement of person (looks like skipping of a word "person". that person = that. "That" here have inherited meaning of a person).

So in "на месте того, о ком она". Того means "person", not a description like that/this. "на месте человека", какого человека? (who/that she is thinking about). Kinda "at the place of that person, that she is thinking about". First that is того and second is кого/о ком.

P.S. I know my explanation is awkward, sorry. ) Not sure, you can understand something from it.