To use EKM for a Bigquery table
You need to create a KMS key with EKM key & use this KMS key for the table's encryption.
When creating a KMS key, please choose Protection Level as External
, then click continue, it asks for uri, then provide your EKM key's uri & create this kms key.
Later follow this guide to use this KMS key on the bigquery table for CMEK encryption