Pledges need to have gift records (installments) tied to the pledge to appear on Gift Reports.  The gift report isn't able to pull the pledges without adding a gift installment for it.

Here is our knowledge base article that outlines how pledges work in DonorDock:  Creating and Managing Pledges 
The system will create installments in the pledge creation by clicking into the Pledge Schedule dropdown and selecting the appropriate option.

You can also edit pledges that are already created as well:

1. Click into the parent pledge details and click the Add button and click Add Gift

Then, in the gift record, change the status to Pledged and Save.  

You can now run a Gift Report and filter to a specific campaign, appeal, etc. and the pledged gifts will appear in the gift data.   
You may also want to add the Pledged Amount column to your gift report as well to see pledged gifts for that campaign.  You do this by clicking the three dots in any column and selecting the check box next to Pledged Amount.

You can also read more about reporting and filtering reports as well: Reports and Filtering Reports