Specify a subnet for SageMaker endpoints

Yes it is possible. Checkout this link for further information into vpc and endpoints. You can also create a VPC endpoint url and connect through CLI as mentioned in this link. In order to obtain the information using CLI you can use the describe-endpoint functionality. Based on the CLI documentation, VPC information might not be available using that.

yes it is possible. please take a look at this link Give SageMaker Access to your VPC . You will need to specify a VPC model with security group for sagemaker to gain access to your VPC by providing at least 2 subnets in different AZ's. To connect sagemaker to an interface endpoint, please look at Connect SageMaker to VPC Interface Endpoints.