If 10,000J  of energy is present at the producer level, then what is the energy available at the T₂ level?

According to the 10 percent law, only 10% of the energy is transferred to each trophic level from its lower trophic level. If 10,000 joules of energy is available to the producer, then only 1000 joules (10000 $\times$10/100=1000) of energy will be available to the primary consumer and only 100 joules  (10000 $\times$10/100=100) of energy will be available to organism.