What is this on my dogs knee? She’s had it for years and whenever I squeeze it, it puts out pimple like secretions. Is it safe to squeeze?

30 33

5 0

10 30

18 30

16 0

20 32

5 0

20 34

9 30

22 32

5 30

4 0

22 31

15 30

27 10

7 30