How to confirm an insert in a plasmid without sequencing?

If you cloned your gene via restriction sites, then you can cleave your ligated vector with the respective enzymes and release your insert. This insert should have the correct size.

Additionally, you can cleave with two restriction enzymes, one of which cuts only in the vector and one of which cuts only in the insert. This way you can check whether you actually have an insert and you get an idea whether it is the right thing.

Also, you could perform a colony PCR with a forward primer for the vector and reverse for insert .

In any case, if your digests look promising you will absolutely have to sequence your insert, even if you are dead sure that you cloned the correct fragment.

This is because by the PCR that you employed to amplify the gene might have introduced mutations (even polymerases such as Pfu produce errors every once in a while).