If you remove the quotation marks from around the column names in the call to aes(), you can get a plot. This solution was mentioned by aosmith in the third post of this thread.
runners <- structure(list(Probanden = 1:6, ventraleK = c(57L, 105L, 46L,
97L, 52L, 118L), dorsaleK = c(60L, 80L, 80L, 59L, 79L, 56L),
lat.Krechts = c(60L, 44L, 61L, 56L, 56L, 7L), lat.Klinks = c(68L,
25L, 39L, 63L, 56L, 25L), Fragebogen = c(4, 0, 10, 1, 19.5,
0), Frage1 = c(2, 0, 0, 1, 7.5, 0), Frage2 = c(2, 0, 2, 0,
7.5, 0), Frage3 = c(0, 0, 5, 0, 4.5, 0), Frage4 = c(0, 0,
3, 0, 0, 0), HuefteR = c(1.16, 1.01, 1.28, 0.79, 1.42, 1.15
), HuefteL = c(1.16, 0.84, 1.46, 0.79, 0.99, 1.15), Balancerechts = c(90.58,
86.27, 74, 104.65, 91.12, 124.21), Balancelinks = c(87.45,
91.5, 78.87, 102.71, 87.87, 111.8), Beschwerden = structure(c(3L,
3L, 3L, 2L, 1L, 2L), .Label = c("links", "No", "rechts"), class = "factor"),
Alter = c(60L, 58L, 48L, 27L, 47L, 37L), BMI = c(18.78, 21.8,
21.15, 20.57, 19.14, 22.09), Geschlecht = structure(c(1L,
1L, 2L, 2L, 1L, 1L), .Label = c("M", "W"), class = "factor"),
X = c(NA, NA, NA, NA, NA, NA), Leistungsniveau = c(3L, 6L,
5L, 9L, 7L, 2L), Trainingsumfang = c(12, 18, 18, 10.05, 14.5,
19)), row.names = c(NA, 6L), class = "data.frame")
library (ggplot2)
scatter<-ggplot(runners, aes(ventraleK,Fragebogen))
scatter+geom_point()+ labs(x= "ventraleK", y= "Fragebogen")
Created on 2020-01-23 by the reprex package (v0.3.0)