我现在正在做这个。这只适用于iOS，而且对我很有效。
将其放入AppDelegate中。

public async override void RegisteredForRemoteNotifications(UIApplication application, NSData token)
{
    if (application.IsRegisteredForRemoteNotifications == true)
    {
        var snsClient = new AmazonSimpleNotificationServiceClient("your aws key id", "your aws secret key", Amazon.RegionEndpoint.YourRegion);

        /* In the AWS SNS example here - https://docs.aws.amazon.com/mobile/sdkforxamarin/developerguide/getting-started-sns-ios.html
           token.Description is used, for me the line below triggers an exception, so I used token.DebugDescription instead.
        */
        var deviceToken = token.DebugDescription.Replace("<", "").Replace(">", "").Replace(" ", "");
        if (!string.IsNullOrEmpty(deviceToken))
        {
            //register with SNS to create an endpoint ARN
            var response = await snsClient.CreatePlatformEndpointAsync(
            new CreatePlatformEndpointRequest
            {
                Token = deviceToken,
                PlatformApplicationArn = "your aws platform application arn"
            });
        }
    }
}

至于将其存储在数据库中，我还没有走那么远，但我正在考虑使用DynamoDb来实现我的特定目的。
当/如果我有Android工作，我会更新我的答案。