In Smartling, spellcheck is included as a QA category. To run QA, go to the Quality Checks tab and click the Check now button. You will get a QA report that looks something like this:

You can select each category to see a more detailed description of the errors. Clicking an error will take you to the string it appears in. You can also see QA errors flagged as you translate and confirm individual segments, so you can choose to address any issues as you go along. However, you should still run a full QA report at the end of the project, to make sure you haven't missed any flagged errors.

If you are required to run QA in an external tool such as Xbench, you will need to export the strings. You can do this under QA Export > Export Job as CSV.