Which of the following methods can be used by a gNodeB to obtain downlink channel...

The correct answers are A. DMRS of the uplink PUSCH of the UE and B. Downlink DMRS signal. According to the official Huawei documentation, gNodeBs can use downlink DMRS signals or the DMRS of the uplink PUSCH of the UE to obtain downlink channel characteristics. The downlink DMRS signals contain information about the downlink channel characteristics, and the DMRS of the uplink PUSCH of the UE can be used to measure the uplink channel characteristics. The uplink SRS and PMI signals reported by the UE are used to determine the uplink channel characteristics. For more information, please see this link: https://www.huawei.com/en/doc/NR-BBU-Design-V1.1/18104301/bbuf-cqi-report.html