Gonna take the bait and give an answer just in case it was a serious question even though original post seemed a bit insincere.
First off, spend some time looking up and observing stuff in the sky. It also helps to know some of the fundamentals that cause normal contrails to begin with. This also gives you something to compare againsts possible chemtrails. Normal contrails, which are untainted, undoctored emission of burnt high-grade kerosene (yes, this constitutes what is generally accepted as a source of air pollution), occur at cruising altitudes of approximately 30,000 feet and higher, where the atmosphere is quite cold such that hot, normal jet exhaust freezes. It's the freezing of the exhaust that allows us to see it for a few seconds, however, this is a momentary condition, as the frozen exhaust crystals quickly thaw, then evaporate, after which the contrail becomes much less visible. Depending on one's eyesight, they may appear totally gone to some, others may still be able to see a faint after image for a few more seconds. Normal contrails are generally visisble for only a 5 to 30 seconds after they've been exhausted.
Chemtrails are typcially dispersed at much lower altitudes then cruising altitudes of commerical air traffic, generally around 10,000 to 20,000 feet. While the type of planes used to disperse chemtrails vary widely, they are generally smaller and specially adapted aircraft much smaller than those that carry hundreds of passengers. In past years though there were also rumors of old military C-type transport planes having been used for chem spraying.
In a previous post, I provided two sample photos, the bottom most which I call to your attention here as it shows two sample trails which I observed before photo'ing. First, a chemtrail was sprayed from top to bottom. You'll have to either not believe me or take my word that the chem spraying plane was already out of view of the camera at the time of the photo, but still within my view. Less than 3 minutes later, a second plane flew by from right to left, still visible in this photoe, which shows the right to left trail to be a normal conntrail - visible for a short distance directly behind the plane, but no longer visible further behind the plane because the this section of the trail has already dissipated. This post can be found here:
Also on yet another post originated from one who admitted to beign a plane mechanic - interesting read at this, I replied with a link to photos of one particular plane that has been specially modified for chem spraying. One alleged plane mechanic's story does not make a puddin, but it defnitely lends weight to this situation. The related mechanic's post can be found here, and will require you to read the entire thread to get to my post and subsequent link of other photos:
Lastly, from observation one will find that while some trails emitted from planes dissipate fairly quickly, others do not. It't the latter that generally are considered to be chem trails, at first notable by the fact that they do not quickly dissipate, then more notable after observation of many minutes to perhaps a period of a few hours, during which one will see how they linger, and while they are lingering they are often morphing into numerous other patterns, some of which can and are often mistaken by casual observers for "clouds", except, they are not clouds. Where this Conspiracy
reality becomes an even a more complex issue is the debate of how these chemtrails - given the wide arsenol of electro-weapons at the disposal of it's perpetrators, can be manipulated to form many of the various cloud-like patterns that they do.