How are you adding your contacts? If you're adding them manually, you will find there is not a drop down option for Job Title but we include it with the First Name/Last Name block shown here:
If you're in the Add Multiple Contacts screen, you will find the Job Title field in these drop down options:
Finally, if you're Uploading a File of contacts, you will find the Job Title field in this view:
Does this help? If not, please provide some additional information on which steps you are taking where you are unable to add Job Title to your contacts.
Also I wanted to add, if you were looking to include the Job Title field within an email campaign you were working on, you would need to make it a Custom Field in order for it to show as a Contact Detail. You can follow our instructions here: Add and Manage Custom Fields.
I hope this helps!