Determining the impact of a monograph is difficult. There isn't a book equivalent of the Journal Impact Factor. Instead, authors need to rely on proxy measures like book reviews, cited by counts, and availability in libraries to demonstrate reach and engagement.
There are two ways to see how many times your book has been cited. Cited by counts for books will always be imprecise because it is impossible to find all the places where your monograph has been cited, but these databases can give you an estimate. Remember that Google Scholar is not a good source for official citation data since there are many mistakes, shadow citations, and the like.
When using WorldCat to calculate availability please note that you may see multiple editions, translations, or formats, of a book. Make sure the holdings you are recording to demonstrate availability accurately reflect the version of the text you are citing.