A citation should provide all the information needed to find a patent; however, not all style guides cover patents, and so the information provided may vary. In general, if you suspect a citation is pointing to a patent, try the following options to track down the patent:
Even if no jurisdiction code is included, a 6-8 digit number in a citation is often an indication that the citation is for a patent. If so, Google Patents can usually quickly retrieve the patent using the number.
The patent owners are usually listed as the "authors" in a citation for a patent. Use the Lens structured patent search to limit your search to the owner, inventor, or assignee.
If the first two options fail, or the information is not provided, try searching for words in the title. The Lens structured patent search lets you limit your search to the title field. It may help to further limit by publication year, if that information is known.
If your citation is for a patent application, your options will be more limited because patent applications have historically not been published. U.S. patent applications began to be published in 2001, so recent applications can be found using the Patent Public Search tool. Some patent applications from other countries can be found using Espacenet, but coverage varies widely by country.
If you are reasonably sure that your citation is pointing to a patent, but none of the above locates the original document, reach out to a librarian!