Marcelo Claure flopped into a chair late this week at WeWork’s headquarters in New York, looking exhausted and exhilarated, his 6-foot-6 frame splayed across the glass meeting room. Mr. Claure, the newly installed executive chairman of the embattled company and a top lieutenant of SoftBank’s Masayoshi Son (who plowed over $10 billion into WeWork), has been preparing to testify in a case brought by a group of state attorneys general challenging T-Mobile’s acquisition of Sprint, where Mr. Claure is also the executive chairman.