One of the menu options under the Contact Overview menu that is accessible when within a contact record is the Know Your Client section of the contact record:
After clicking Know Your Client, you'll then see the Know Your Client area for the contact and can begin filling in your applicable information for them.
Here, let's look at the Professional Contacts section of this page:
If no data has been entered here, it will be blank as above. To add data, just click the Edit button in the top right corner of this section. You'll then see the below:
You can then begin typing a Professional Contact's Name (Last or First Name) and you should see contact name options from your database appear to select the correct one. Professional Contacts must have their own database records in order to be selected here. After making selections for any or all of these fields, simply click Save Professional Contacts. This area might then look similar to the below:
Each of the Professional Contacts listed in this area can be accessed by simply clicking on their name.
Note: Each of the Professional Contact fields can be included in any Custom Exports you build.