Here’s a list of 100 topics in digital marketing:

1. Search Engine Optimization (SEO)
2. Keyword research
3. On-page optimization
4. Off-page optimization
5. Link building
6. Local SEO
7. Mobile optimization
8. Technical SEO
9. Voice search optimization
10. Google My Business optimization
11. Pay-Per-Click (PPC) advertising
12. Google Ads
13. Facebook Ads
14. Instagram Ads
15. LinkedIn Ads
16. Twitter Ads
17. Display advertising
18. Video advertising
19. Shopping ads
20. Remarketing
21. Social Media Marketing (SMM)
22. Facebook marketing
23. Instagram marketing
24. Twitter marketing
25. LinkedIn marketing
26. Pinterest marketing
27. YouTube marketing
28. Social media analytics
29. Content Marketing
30. Blogging
31. Infographics
32. Podcasts
33. E-books
34. Whitepapers
35. Case studies
36. User-generated content (UGC)
37. Guest blogging
38. Email Marketing
39. Email list building
40. Email segmentation
41. Email automation
42. Email personalization
43. A/B testing
44. Mobile Marketing
45. Mobile app marketing
46. SMS marketing
47. Push notifications
48. In-app advertising
49. Video Marketing
50. YouTube advertising
51. Facebook video advertising
52. Instagram video advertising
53. Live streaming
54. Influencer Marketing
55. Influencer identification
56. Influencer outreach
57. Influencer agreements
58. Micro-influencers
59. Affiliate Marketing
60. Affiliate program creation
61. Affiliate program management
62. Affiliate network selection
63. Website Design and Development
64. User experience (UX) design
65. User interface (UI) design
66. Responsive design
67. Landing page optimization
68. Conversion rate optimization (CRO)
69. Customer Relationship Management (CRM)
70. CRM software selection
71. Lead management
72. Sales funnel optimization
73. Analytics and Reporting
74. Google Analytics
75. Social media analytics
76. A/B testing
77. Data visualization
78. E-commerce and Online Retailing
79. E-commerce platform selection
80. Online store design
81. Shopping cart optimization
82. Payment processing
83. Shipping and fulfillment
84. Local SEO and Online Listings
85. Google Maps optimization
86. Online review management
87. Citation building
88. Local content creation
89. Conversion Rate Optimization (CRO)
90. A/B testing
91. Heatmap analysis
92. User testing
93. Multivariate testing
94. Branding and Reputation Management
95. Brand strategy
96. Brand messaging
97. Online reputation management (ORM)
98. Crisis management
99. Marketing Automation and AI
100. Marketing automation tools.

Note that this is not an exhaustive list, and there are many other topics within digital marketing that could be included as well.