Can I show signature fields based on the number of selected options in a dropdown?

How can I have the same number of signature requests as to employees chosen.

Yes, it is indeed possible to do so. First off, I assume you're referring to the field  "Who are the workers on site" on your form. 

If so, then you will need to do the following: 

1. Assign a calculation value to each option on your drop down, the value must be 1 for all the options, this guide will help you doing so: https://www.jotform.com/help/301-How-to-Assign-Calculation-Value 

2. Once you're done, add a Form Calculation widget to your form and just include the drop down field in it: 

3. You will then know how many options have been selected in the drop down, now you will need to add as many signature fields as options on your drop down you have. 

How-to-Add-an-E-Signature-to-Your-Form

4. The last step will be to set up conditions and show the signature fields based on the number of selected options, this guide will help you with that: https://www.jotform.com/help/316-How-to-Show-or-Hide-Fields-Base-on-User-s-Answer 

I hope this helps.