eJuice comes in many varieties. You can get 0 nic ejuice, juice with nicotine or (in many places) juice that has other substances. If you were tested for drugs, you'd probably test positive for whatever you vaped. Depending on your juice, that would be nothing, nicotine or whatever other substance you vaped.
If nicotine vaping is legal wherever you are now and you vaped non-black market nicotine ejuice, you'd have nicotine in your system but it shouldn't be distinguishable from nicotine from smoking cigarettes. I'd make sure to stay away from anything black market as it might be laced or cross-contaminated with something else. If you're really worried about it, it would probably be best to avoid all those risks by not vaping at all.