How to Query Metadata Components By using SOQL in Salesforce ?

@Rocks_SFDC
You need to use tooling API for that. Here is the documentation: https://developer.salesforce.com/docs/atlas.en-us.api_tooling.meta/api_tooling/
Andrew wrote an APEX wrapper to it which is readily available to use here: https://github.com/afawcett/apex-toolingapi