How do I clear the entire system of all my testing data?

Jobs, requests, custom offers and users can be deleted from admin dashboard.
For rest of the data you need to clear below mentioned tables from database:

- wp_job_admin_earnings 
- wp_job_affiliate_commissions 
- wp_job_affiliate_transactions 
- wp_job_affiliate_users 
- wp_job_braintree_merchant_ac_ids 
- wp_job_chatbox 
- wp_job_credits_balance_log 
- wp_job_custom_extra_orders 
- wp_job_discounts 
- wp_job_discount_codes 
- wp_job_featured_orders 
- wp_job_invoice_business_info 
- wp_job_ipcache 
- wp_job_likes 
- wp_job_orders 
- wp_job_orders_arbitration 
- wp_job_orders_extended_delivery_time
- wp_job_payment_gateway_log 
- wp_job_payment_received 
- wp_job_payment_transactions 
- wp_job_pm 
- wp_job_ratings 
- wp_job_ratings_by_seller 
- wp_job_subscriptions 
- wp_job_subscription_orders 
- wp_job_tips_orders 
- wp_job_topup_orders 
- wp_job_topup_packages 
- wp_job_transactions 
- wp_job_uservacation 
- wp_job_var_costs
- wp_job_withdraw

To clear the tables you just need to truncate the tables.

Click on the table name, then click on operations tab as shown below:

then scroll down and you will see the option to empty the table as shown below:

We strongly recommend to make database backup before you make any changes in database in case of any issues.

If someone wants to keep few users but wants to delete their data stored in usermeta:

You can use plugin and steps mentioned in below link to delete the data related to the users you want to keep.