I just wanted to ask how much fork travel does this bike have and is it worthy of buying??
Information about fork travel should be present in marketing materials to a bicycle. If you are looking at a web shop page, such information is usually hidden somewhere in the lower part of a page.
Alternatively, the travel is usually specified somewhere on the fork itself. If you could see the bicycle in person or ask the seller, that would be the most reliable method.
The provided picture is in quite low resolution, which does not allow to recognize the brand of frame, fork, or other essential details. Neither it helps to see any inscriptions on the fork.
Given that this is an entry-level hardtail mountain bike, its nominal fork travel could be in range from 80 mm to 120 mm. Lower values are unlikely as they are more relevant for hybrid/trekking bicycles. Longer travel is unlikely because longer travel hardtails are less popular and typically more high tier. I'd wager it has 100 mm of travel, as it is the most popular value for such machines.
Whether it is not worth buying anything or not is up for the potential buyer to decide. I doubt we can give you an advice here, especially given how little information about anything is given.
A way to gauge the amount of travel a fork has, in the absence of any other information or clues, is to measure the amount of exposed stanchion. A stanchion is the upper part of a side of the fork which is very smooth and narrower than the lowers. The stanchions are what the lower fork slides up and down on during compression and rebound. Most forks have approximately 10mm of exposed stanchion that is unused as far as travel. So if you were to take a measurement of the exposed stanchion from the bottom of the crown to the top of the lip of the lower fork seal and it measures, for example, 110mm, you are likely looking at a fork that has 100mm of travel.
In almost all cases, a suspension fork has travel anywhere from 80 to 200mm in increments of 10mm. If you have an air spring suspension fork--which can be determined by the presence of a Schraeder valve for air input or removal on top of the left fork leg-- the air can be let out via the valve while fully compressing the fork to bottom out. When the fully compressed, measure the remaining exposed stanchion, subtract this figure from the length of exposed stanchion when fork is pumped up to the recommended pressure for your riding weight. The difference between the measurements is the amount of travel.