Copy both Spark Connector and Mongo-Java-Driver among your datanodes, ( Nodes where your spark executors / driver are supposed to be running ). The Spark Connector uses the Mongo-Java-Driver and the driver will need to be configured to work with SSL. See the ssl tutorial in the java documentation.
OBS: Find yours at the mongodb website.
2) Go to ambari > Spark > Custom spark-defaults, now pass these two parameters in order to make spark (executors/driver) aware about the certificates.