My printer came with a knock off BuildTak like build surface. What can I use to clean it? I don't want to damage it.
For BuildTak, my first recommendation is isopropyl alcohol (aka rubbing alcohol or isopropanol). Readily available just about anywhere basic medical supplies are sold, it cuts though light oils and greases, and dissolves most common build surface adhesives like hairspray or Elmer's glue stick. In fact I often give my Ender's bed a light spray of isopropyl after an initial layer of hairspray, as the alcohol thins the hairspray a bit so I can take a plastic scraper and spread it around a little more evenly, before it sets to a very tacky initial surface that holds well.
Depending on where you live, denatured alcohol aka methyated spirits might be easier to get, and this stuff also works well as a cleaner and degreaser. The methanol does a little better job at actually removing old build adhesive instead of just "reactivating" it, and it also seems to do a little better than isopropyl at releasing and capturing old print residues that didn't make it off the surface with the rest of the print.
Be aware that both the liquid and the vapors of both of these are toxic, denatured alcohol a little more so than isopropanol. You should have plenty of ventilation through your workspace while using either one.
For a deep clean, especially with a removable build surface, it's hard to beat a mild dish detergent and water, and a scrub with a Teflon-safe Scotch-Brite sponge (they're usually blue). A clean rinse, pat dry with a towel, then give it a spray of isopropanol to finish drying it and it's ready to go. This is more of a hassle and I don't recommend it as a quick between-prints cleaning, but it can bring a well-used bed surface right back to life when more volatile cleaning agents won't do it.
Whether it's worth the frustration getting the plate properly rinsed (soap, being slippery, is not going to aid adhesion), versus just scraping the surface back off and putting a new one on, depends on how easy it is to bring the bed surface to the sink. My Ender's magnetic surface makes this much easier than a simple adhesive-backed surface right on the aluminum. By the same token it also makes the surface easier to replace, and they're not that expensive (so I highly recommend them if you like BuildTak), but \$12 is \$12, compared to 5 minutes in the sink with some Palmolive.
Besides IPA (80 %), which is one of the best cleaners for general pourpose, 99 % ethanol ("Spiritus") can work as a good substitute.
Acetone too can be used on BuildTak and its clones in a pitch without damaging it, as long as it is kept away from the edges, where it could weaken the bond to the aluminium. Using it repeatedly could however smooth the surface over some.
Mineral Spirits might be useful to prepare the aluminium for a new bed, but sould not be used on the BuildTak or its clones, as it could harm the surface and leave residue.