The zig zag structure on the left - that is an antenna, and the chip your arrow is pointing to - what pin on the device is it connected to? That will give you the best idea of what it is.
The pictured antenna on the top is a size reduced broadband monopole, its polarized vertically if that board is facing such that the pigtail, with its u.fl connector goes downward. Its vertical is the direction to the left. That should be facing upward. Then it will be omnidirectional with the strongest signal at the horizon and possibly above, which is likely what you want, Otherwise it would be horizontally polarized and directional off of the two broad sides.
The chip pointed to by your arrow? Maybe its for RF, or quite possibly it is not. Is it in the signal path for the device its next to? Its datasheet will likely tell you what is likely connected to that pin.
You can build your own antennas into your design - or build in a connector and make or buy them.
Yes, the frequencies are the same for 2.4 GHz wifi so you could use any wifi antenna.
Or use a piece of straight wire extending up into free space 1/4 wavelength long. That and a ground plane for the RF ground would be a good starting point.
Best to know a bit about antennas so you can ascertain what kind of antenna would work best in your applications. The wikipedia page on antennas is a pretty good start.
https://en.wikipedia.org/wiki/AntennaOne thing to keep in mind is that the loss in a thin coaxial cable such as a pigtail at 2.4 GHz is going to be significant for any long transmission line.
That why they tend to be short.
Another thing you should consider is - If your receiver is a device which may have some RF noise associated with it (possibly from its power supply, if it uses dc-dc conversion) or similar setups. If so using an antenna thats physically separated from it a bit may improve reception.
You can easily buy add on antennas with pigtails (like the ones in your picture) but to use them you will need to add an antenna connector to your design and possibly match it to your output appropriately. Two kinds of antenna connectors are the most popular / best choices at 2.4 GHz devices, u.fl (which you pictured) and SMA.
u.fl connectors cant be repeatedly plugged in or unplugged and remain viable, figure they can handle maybe at the most 20 plugging/unplugging cycles, so only use them if your antenna is unlikely to be changed often.
Use an SMA if you plan on using different antennas and changing them as needed.
2.4 GHz antennas are small and generally fairly easy to make, and there are a lot of different plans you can build that work well online. For nearby you likely want an
omnidirectional antenna. But what
polarization will you need? A vertical
quarter wave monopole at 2.4 GHz would be one option and very simple, it could be as simple as a wire that extends
up from a PCB. But what if you dont know how the PCB will be used? (which way the user will face up?)
Probably the most popular option is similar to what you showed, a
microstrip antenna with what is called a
meander line for size reduction. You could also wind your antenna into a helical shape to reduce its size a little bit.
There is a lot of information on the web to get you started. Many books on subjects like microstrip antennas can be found online. The complete design process can be found fully explained in the form of theses from students seeking their degrees. For example, I just found "Small Antennas Design for 2.4 GHz Applications" by Ibrahim Turki Nassar which shows the math.
Or you can put an antenna connector on your board and experiment. Thats what I would suggest if you want to learn about antennas.