I had to guess what your data look like, so I hope this is close enough.
library(ggplot2)
library(dplyr, warn.conflicts = FALSE)
DF <- data.frame(date_enrollment = c("2021-03-01","2021-03-01","2021-03-01","2021-03-01",
"2021-03-01","2021-03-01","2021-03-02","2021-03-02",
"2021-03-02","2021-03-02","2021-03-02"),
data_collector = c("A", "A", "B", "B", "B", "B", "A", "A", "A", "A", "B"))
Totals <- DF %>% group_by(date_enrollment) %>% summarize(N = n())
#> `summarise()` ungrouping output (override with `.groups` argument)
ggplot(DF, aes(date_enrollment)) + geom_bar(aes(fill = data_collector)) +
geom_text(aes(y = N + 1, label = N), data = Totals)

Created on 2021-03-30 by the reprex package (v0.3.0)