Final answer:
The regular reporting senior typically endorses the appropriate block for a concurrent/regular report, which might be block 3, but the exact block depends on the specific form and its instructions.
Step-by-step explanation:
The question relates to how a regular reporting senior should endorse a concurrent/regular report in a performance evaluation or similar official documentation. Specifically, within the context of military or organizational reports, the regular reporting senior would mark the appropriate block to endorse a concurrent/regular copy. While the precise block number may depend on the form being used, in many evaluation forms, block 3 is commonly designated for the reporting senior's endorsement. However, without knowing the specific context or form in question, one cannot provide an absolutely definitive answer. It's essential to consult the instructions of the specific evaluation form in use to determine the correct block for the endorsement.