To check if your preprint has received any citations use: Lens, Dimensions, or Google Scholar. You might as well check the preprint server where you uploaded your preprint as some preprint servers mention citations as well. For altmetrics, check Dimensions – tracking a subset of available preprint servers – or check the preprint server as many display altmetrics and usage data like views and downloads for individual preprints, and reviews and comments (when supported). To check which commenting or annotation options a preprint server offers, and which (alt-) metrics are collected, check ASAPbio, which curates a list of preprint servers in all domains.

However, be cautious when using usage data, and only use them when they are exceptionally high which is often difficult to judge.

Note that Research Information portal shows PlumX and Altmetric Explorer altmetrics only for a limited number of preprint(s), as many are not (yet) registered in the research information system Pure. Scopus does index preprints (only shown in author profiles), but it does not track citations to and from preprints, nor calculates a FWCI for a preprint. You might try the ‘Cited Reference search’ in the Web of Science, but the search will only tell how often your preprint has been cited in articles published in journals indexed by the Web of Science.

Citations, raw counts: Dimensions, Google Scholar, Lens
Altmetrics: Altmetric bookmarklet, Altmetric Explorer (via library databases), depends on preprint server
Views: depends on preprint server
Downloads: depends on preprint server
Reviews or comments: depends on preprint server