Retrieving the logs for a specific user using Sucuri’s data is not a good idea, we store the data linearly without additional associations, this approach works very well for us because because the Sucuri plugin has no need to apply filters (which is what you need for your project).
My suggestion is to implement your own user login detector [1], that way you can take control over your own data and will remove the dependency on a 3rd-party data storage system that was designed with a different goal. Having your own data plan will also allow you to have better performance for your use case.
However, if you still plan to use Sucuri’s data for this, you can call this function [2] and iterate through the results to find the logs associated to a specific user ID. If you want to rely on the data from the API service, you can do the same but with this other function [3]. But again, do not do this if you care about performance, if you are going to query a small amount of user accounts it will be okay, but if you need to execute this query multiple times against many users IDs it will be better to have your own data plan.
[1] https://github.com/Sucuri/sucuri-wordpress-plugin/blob/8542b2f/src/lastlogins.php#L233-L256
[2] https://github.com/Sucuri/sucuri-wordpress-plugin/blob/8542b2f/src/lastlogins.php#L259-L270
[3] https://github.com/Sucuri/sucuri-wordpress-plugin/blob/8542b2f/src/api.lib.php#L442-L460