Design primers that flank the Cas9 cut site and look for a change in band size.

Robert Adolf Brinzer Thank you, but how to show Cas9 or Hpt positive plants in T0?

Hpt confers hygromycin resistance so can be used as a marker gene. Use hygromycin selection and all surviving plants should be what you want. If you really need to PCR your plasmid genes as a positive control you can just use the plasmid sequence to design primers and then BLAST them against the genome of your plant.