It's been a while since forevermore solved his problem and, because they did not post their solution...
Install Realtek d723 WiFi
sudo apt-get install linux-headers-`uname -r`
sudo apt-get install git build-essential dkms
git clone -b extended --single-branch https://github.com/lwfinger/rtlwifi_new.git
sudo dkms add rtlwifi_new
sudo dkms install rtlwifi-...
Depending on the age of your system, Installing the Ubuntu Bionic Beaver hardware enablement stack might help you.
Otherwise try following the troubleshooting wireless on Ubuntu (since elementary OS uses Ubuntu for it's base)
if it is a broadcom card there's a good chance you'll need to install an external driver.
If your computer isn't showing WiFi at all, you may need to find a driver for your WiFi card. Do a Google search for your make and model and see if someone has built something or has a solution for it. Ubuntu forums are really helpful for this since Juno is built on 18.04.
Also, sometimes my wifi just stops working and running service network-manager ...
Looking at your laptop from the spec sheet I found on HP's site, it looks like you have an Intel powered wired internet connection card, but your WiFi card is made by Broadcom. It's pretty common for boards to have network adapters from different manufactures but since the WiFi one is what's acting up, you likely need a Broadcom specific driver.
I found a ...
Did you install the proper driver for your wifi adaptor? Maybe you can find some information in ubuntu forum like this,