Adding an E-signature to a job application

How you do that depends on a number of things. In what format is this application? PDF? Word? Something on the web? If it's a PDF, what application are you using to try to sign it?

If you're using Preview, see here:

Fill out and sign PDF forms in Preview on Mac - Apple Support

When in doubt, contact whoever is requesting the signature.

Is an E-signature actually required in the job posting. If they didn't specifically ask for it, don't bother as the job application will be software scanned for content long before any human eyes read it — unless it is going directly to the hiring authority by pre-arrangement.

You will need to provide a bit more detail. Job application for what? What form/file format is it? How is it being submitted? Etc.