When you add a new system under HANA Studio, below screen comes where different folders are available to manage HANA system. To open SQL editor, you have to select HANA system and click on SQL button at the top.
Once you click on SQL button to open SQL console for selected items, right side you can see a SQL editor where you can run SQL queries in HANA database.
You can also open SQL console by right click on HANA system HDB → Open SQL Console. When console is opened, at the top you can see host name and instance number and also schema name where the database objects will be created.